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Use of RO, DI, Softwater in Aquariums


By Carl Strohmeyer-PAMR 40+ years experience
Updated 8-5-23

INDEX of this article:

Which system should an aquarium keeper use, RO, DI or both OVERVIEW:

While the use of Reverse Osmosis and/or De-ionized water has been around for quite some time, their use has exploded of late, often for good reasons, but unfortunately there is a lot of miss-information about how these systems work (including in a popular YouTube video) and gimmicky products that over sell the less experienced aquarium keeper.
I have used both types of equipment over the last few decades, and this includes variations within such as the use of Cellulose acetate membranes which are the oldest form of commercial RO membranes, yet still used along with lower quality TFC membranes, in most RO and RO/DI combinations to keep the price MUCH lower!

Re-mineralization after use of RO and/or DI water and essential minor and trace elements/minerals is also discussed.

I also address the use of water that has passed through typical home/office water softeners and why the use of such water poses a serious long term threat to ANY fish' health.

Here is a basic video about this subject:
Do I Really Need Aquarium RODI
Do I Really Need Aquarium RODI? With A Catch...



Reverse Osmosis System

RO/Reverse Osmosis water is simply water that is run under pressure through a micron pre-filter, then a carbon pre-filter & finally a osmonic membrane.
For reef keepers, these are often a must and at a cost of just pennies per gallon, often well worth the investment over paying .25 cents per gallon.
For Discus keepers and similar biotope aquarium RO or RO/DI units can also be helpful.

The membrane is the most expensive part of a RO unit and is rated in gallons per day (gpd).
With water that is too hot or cold (the ideal operating temperature is between 70-80 F or 21-27 C), along with low water pressure (psi), and high TDS (total dissolved solids) all will combine to slow the rated capacity of a RO Unit & membrane. High TDS will also affect the life of the membrane.
Often the pressure provided by the tap water is adequate, however with high capacity RO Units additional boost pumps are required (usually units over 100 gpd which require 65 to 80 psi).

The few top quality aquarium RO units still produced use TFC Medical Grade (thin film composite, sold by Pentair USA) membranes which is much better for removal of ammonia, phosphates, herbicides, pesticides, and TDS.

Other units still utilize the popular Economy TFC membranes sold by Dow under the Trade Mark of FilmTec. This includes the Coralife, which I have considerable experience with along with Bulk Reef Supply & many others.

The other common type is the CTA, a.k.a. the cellulose triacetate membrane (also sold by Dow & others) which is used in low cost RO units commonly sold by discounters such as Amazon. Cellulose acetate membranes are the oldest form of commercial RO membranes and the lowest cost to produce, hence the much lower costs of systems utilizing these.

For those thinking they may have gotten a good deal on a RO system that claims to use a TFC membrane, I will remind readers of basic economics and that is while many sellers will price a system low to get a customer and then make the money on parts (think about the cost of HP printers, then the cost of replacement ink), if the replacement parts are at or near the cost of a top quality TFC membrane, then you do NOT have a unit/system utilizing a top quality membrane.
I have used many different RO units and the the results (before passing through a DI chamber) in higher waste water, higher TDS and other measurable aspects such as GH are notable.

Below is a screen-shot from the manufacture/distributor order web site of the cost a retailer will pay for these items Pentair membranes. If the replacement retail price is at or near these prices, then unless it is a clearance item, it is not a high quality TFC membrane (simple economics 101):
Actual wholesale cost of a TFC RO membrane

I, along with the person who purchased my aquarium maintenance, research, and design company have used the Coralife RO and RO/DI systems. While they claim to use the TFC, our results were not the same as with other units that cost considerably more for the membrane, which again brings up the argument that I can purchase wholesale a 100 GPD Coralife membrane for $25 (or less) but the better Pentair USA medical grade membrane used by several high end RO and RO/DI systems have a wholesale cost of $50.

Keep in mind too that FilmTec is a Dow Trademark and does NOT mean this is a TFC Membrane or if it is, the best TFC since price determines quality here.
The Filmtec can be either the TFC or CTA. The Dow Economy FILMTEC FT30 Membranes are TFC, however many models are not, so make sure to do your homework and apply common sense logic as per economics whether it is the CTA, TFA or a better medical grade TFC such as the Pentair USA TFC Membrane.
Example Reference: Filmtec Cellulose Triacetate Membrane

Premium Aquarium RO System in operation showing efficiency of micron fiber
A test of an RO or RO/DI system/filter is if the reject water is higher than three gallons of water for every one gallon I would question the quality of the membrane used. This can result in concentration of ammonia as I have noted in experiments in the past.

Also be aware that CTA membranes lower permeability requires higher pressures so booster pumps may be needed for optimum efficiency.
This is especially true if you use a RO system that uses twin membranes as a way to increase output while keeping the purchase cost lower than would be the case with a higher GPD membrane.
Even with a TFC membrane (regardless of membrane quality), I do not advise twin membrane systems as this increases the pressure needed to run the system, often complicating the system or lowering efficiency if a booster pump is not added.

Both membranes are damaged by chlorine, which is one reason for the carbon pre-filter (canister).
The membrane should be changed every 2-3 years or 12,000-18,000 of total water produced (whichever occurs first).

A properly functioning membrane will work effectively after a 2-3 gallon break-in (throw this water out), after this initial start up, you should have 1 gallon of "good" water for every 3 gallons of reject water. If higher, this can concentrate molecules that the RO membrane cannot remove (which is why spending a few extra $$ for a good RO unit such as the TMC designed specifically for aquarium use is worth it, not looking for the best deal via eBay, Amazon, or popular Aquarium Supply discounters).

Aquarium RO, RODI TDS ResultsTo the right is proof that the quality on many levels of the RO system affects simple RO results.
Here you see a high TDS before and ZERO TDS after WITHOUT EVER USING A DI Chamber!!
This is using the ultra premium AAP/TMC RO System.

RO System Product Resource: Tropic Marine Centre V2 Pure Reverse Osmosis System using Pentai USA Membranes

TDS Monitor Resource: TMC Total Dissolved Solids Monitor

Generally speaking, a well maintained RO unit will reject about 97%+ of TDS.


*DI Unit; which stand for "De-Ionized".
Most commercially available DI units are simply a RO unit with an additional DI canister/chamber following the RO membrane (API makes a basic DI only unit though). This chamber utilizes resins that further remove TDS from water.
With this system, you can achieve 0 mineral cations and a TDS of 0 after starting with tap water over 250 TDS, while this same tap water run through a RO only unit would generally result in about 7 TDS at most with a quality RO only system (I average only 2-3 TDS with the "top of the line" AAP/TMC RO System).
You will also achieve a pH of 7 since a DI unit or chamber affects ionization where as a RO by itself does not.

For my purposes I found that a well designed TFC (thin film composite) RO only unit was/is more than adequate, however if you are making water for extremely sensitive purposes (such as a car battery), or have high ammonia levels in your tap water, a DI/RO unit may be the better choice for you over a RO only unit.
The reason is much of what the additional DI chamber/resin removes is mineral cations as well as all charged molecules (electrolytes).

Which is why DI water is better for a car battery, but these few mineral cations missed by RO only units are not a problem for any freshwater or saltwater aquarium (unless run off from a Home/Office Water Softener) and in fact these ions are generally beneficial.
As well the operating costs of DI chambers are very high as I have had to replace the resins in these chambers as frequently as once per week with some units under high use.

API Tap Water Filter Basic De-ionization filter
Another alternative is the "API Tap Water Filter" which is nothing more than a large disposable de-ionization resin filter with built in carbon and filter floss. With this filter you basically throw way 90% of the filter when exhausted.
This filter does not utilize any other chambers or RO membranes of any type.
The API Tap Water De-Ionization Filter is a very economical way to purchase such a filter, but very expensive long term. I have used these and found the chamber is only good for about 100 gallons of water, which is not a bad deal for a Betta keeper desiring to mix pure water or cut their tap water, but it makes little sense for a Reefer, Discus Keeper, or Planted Aquarium Keeper that needs volumes or water.

The bottom line is to NOT believe the some of the hype some sellers of Four to Six Stage RO/DI units put forth and save your money (both initially and ongoing) and purchase a QUALITY TFC RO only water system which WILL result in 0 phosphates, 0 nitrates, and chloramines along with very low TDS readings with less reject water and lower operating costs.
I will also state that these Four to Six Stage RO/DI systems are certainly not bad either, only that why spend the money, including ongoing DI resin replacement for a good RO/DI system when a better RO system is all you need??

There is a good reason some of these 4-6 stage RO/DI units can be sold at prices comparable to or even lower than top quality TFC 3 stage RO systems and and this is the use of (consider these points before falling for the gimmicks):

What you will get is a long term higher operating cost since replacement resins are not cheap, and again in most aquarium applications, not necessary as per my own long term and extensive use and testing!

As noted earlier, another test of an RO or RO/DI system/filter is if the reject water is higher than three gallons of water for every one gallon I would question the quality of the membrane used. This can result in concentration of ammonia as I have noted in experiments in the past.
Often these economy RO/DI systems sold by popular discounters will have higher reject water.

There are really only two MAYBE reasons to purchase a unit that also features de-ionization:

  1. If your tap water has high ammonia or is in a municipality that uses chloramines (such as some SW USA locations). An expensive to operate DI chamber are often are only good for about 50 gallons and make little difference for chloramines if well designed (some of the cheap Amazon/eBay units are not).

    If the RO unit is well designed using quality catalytic carbon (such as the TMC models), the fact is these will remove chloramines.

    *Removing Chloramines from Water
    * Catalytic Carbon for Chloramine Removal

  2. You want to run your system directly off from a home or office water softener that uses sodium chloride or potassium chloride, since these systems radically alter the mineral ions in ways detrimental to fish and invertebrates (reference section about use of home water softeners later in this article).
    The use of an RO system only will not remove much of the sodium ions that can be detrimental to your aquarium health (which includes osmotic function of fish).
    In fact this is a case where by the use of an RO/DI system, operating costs would actually be lower than an RO only that is run off from tap water or well water.


This is another aspect of misinformation is what is removed by a particular component of an RO or RO/DI system. This misinformation is even spread by one of the largest sellers online of large RO/DI systems that are often not necessary for aquarium use, both freshwater and salt water, but based on this misinformation, many are unfortunately convinced that they need these additional components.

This list below is based on a properly functioning RO/DI system, as often additional modules of water purification are needed if one module/component does not completely remove undesirable elements of input water such as nitrates.

  1. Sediment/Micron Pre-Filter;
    The main purpose of this chamber/component of a RO/DI system is to remove sediments such as rust from the water.
    From my experience, these sediment filters generally range from 1 to 20 micron in pore size.
    These should be changed frequently to maintain pressure for the rest of the unit as well as extend the life of the membrane. How often you need to change it can vary greatly.
    What my experience has shown me that changing of the micron cartridge has little bearing on the life of the resin in a the DI chamber (if a DI chamber is even used).

    If the water coming in to the RO or RO/DI system contains a lot of sediment such as rust or large sediment particles, multiple stages or better; a separate sediment system is best added (rather than make the mistake of purchasing multiple stages of filtration after the sediment filter).
    Adding a 20 micron pre-filter (purchased at Home Depot, etc.) to your existing RO system can help considerably. Or even better, adding a whole house system such as this one to remove rust, iron, etc.

    The above is a more cost efficient solution when one is looking long term at water that is high in TDS and sediment rather than the 6 stage or larger RO/DI systems sold by popular aquarium supply retailers that do not properly address the cause of such issues with stepped down micron filters.

  2. Carbon Filter;
    When a good quality catalytic carbon filter block is part of your RO system, it removes many chemicals, toxins, chlorine and YES chloramines assuming a quality catalytic carbon filter block is used in the system.
    Unfortunately this aspect is missed in a popular YouTube video promoting more elaborate systems

  3. Reverse Osmosis (RO) Membrane;
    Properly functioning Reverse Osmosis (RO) Membrane for aquarium use I have already gone into great detail what makes a good membrane, so I am going to assume an optimum quality membrane here.
    The main purpose of the membrane is removal of mineral salts, which at the proper water pressure and temperature an optimum membrane is VERY efficient at doing.
    This same membrane can also remove most nitrates and ammonia. In fact my own tests over the years showed 100% removal of nitrates.
    However some claim nitrates can get through, but this again falls back partly to the membrane used, as my results varied with systems such as the Coralife RO system using the FilmTec membrane which is also used in many popular RO/DI systems, did in fact leave some residual nitrates while the TMC V2 system had 0 nitrates.
    I should note that these results may also be part of the system design too such as how the system maintains water pressure to the membrane.
    It should also be noted that any membrane is only as good as the sediment and carbon pre-filters.

    The picture to the right shows how a properly functioning RO membrane rejects sodium ion while allowing water molecules to pass.

  4. De-Ionized (DI) Module/Chamber;
    A DI resin chamber traps all charged molecules passing through it, and leaves uncharged (neutral) molecules free to pass through.
    Water, for example, passes through it, as would other uncharged inorganic molecules such as oxygen (O2). Ions and minerals salts missed by the carbon & some RO membrane such as sodium (Na+), copper (Cu++ or Cu+), ammonium (NH4+), phosphate (PO4---), silicate (Si(OH)3O-), and acetate (CH3CO2-) generally get caught (assuming the resin is not depleted).

    The result is usually pH neutral water unlike the water coming from even the best of RO only systems.
    The DI resin chamber can also be a good back up from nitrates, chloramines, and in particular ammonia/ammonium missed by the earlier chambers.

Further References:
Reverse Osmosis/Deionization Systems to Purify Tap Water for Aquaria
Removing Chloramines from Water


Another method to prepare DI Water is to distil the water by boiling then collecting the condensation of this water (AKA distilling).

This can be an economical DIY project or there are commercial water distillers also available.
If you are making a DIY Water Distiller, make sure to use condensation collection coils & other related surfaces that will not add elements back into the water, especially copper coils (which can defeat the purpose of the water distiller).
Some plastics can also add chemicals back into your water, generally stainless steel is accepted to be the best surface to use for condensation collection.
Please click on the picture to enlarge

Betta Tank with RO Water, Correct Use Use of RO, DI (Distilled) water in Aquariums or Betta Tanks;

Do NOT use 100% RO water unless you are an advanced fish keeper with time on your hands, which includes having GH and KH Test Kits/Strips, as well as some basic knowledge or aptitude of chemistry.

Generally the use of RO or DI water in freshwater aquariums should be restricted to blending with tap or well water so as to "Cut" the water resulting in lower buffers and hardness of aquarium for use with Amazon River, Southeast Asia (such as Bettas), or similar fish.

Generally I start with 25% RO water and work up from this over time (if necessary).
The reason is that RO and similar water is NOT properly mineralized for correct osmoregulation with essential minerals such as calcium nor is there any carbonate buffers to maintain a stable pH which the lack there of would result in a roller coaster pH in the aquarium, often with disastrous results.

That said, for advanced freshwater fish keepers who desire exact Amazon River or SE Asia aquariums (or even Goldfish, Livebearers, etc.);
The use of 100% RO water can achieve phenomenal results providing all trace and major minerals as well as buffers are replaced (buffers are very often missed with users of 100% RO Water).
The reason is that you can reproduce the exact water conditions you desire (assuming again you are familiar with water chemistry), without starting from a point of incorrect minerals or even high nitrogenous organic compounds such as Nitrates (which are often found in tap water or well water).

Everything you need to know about water chemistry:
Aquarium Chemistry

With Marine Reef Aquariums, since most better salt mixes are exacting in their mineral and trace element blends, the use of RO water provides for better results.
More importantly, topping off for evaporation in marine aquariums with tap water (even fish only tanks), results in climbing nitrates, sometimes falling alkaline reserve, incorrect usable calcium levels, and more. So the use of RO or DI water is often a must in marine aquariums for evaporation from my experience.

Correct use of RO Water:

First, if small amounts RO Water (under 25-50%) is used to "Cut" hard/alkaline tap/well water, often only electrolytes with mild buffers already added such as SeaChem Replenish is all that is necessary, not strong buffers or baking soda.

For those considering using RO or DI water in higher amounts, it is important to note that for proper osmotic function trace amounts of several minerals are required.
Many of these supplied simply by water changes and supplements such as Wonder Shells.
For this reason pure RO (Reverse Osmosis) or Distilled water are not good for water changes unless re-mineralized (with products such as Replenish, Wonder Shells, and Buffers) or blended with tap or well water that is possibly too high in many minerals (a very high GH over 500 ppm can slow respiration in some freshwater fish).

To use with RO water:
*Aquarium Mineral Blocks
*SeaChem Replenish; water RO, DI mineral, carbonate replenisher
*SeaChem Aquarium Buffers

For Alkaline/Acid Buffer Ratios for use in Planted, Amazon, or SE Asian Aquariums (softer, low pH aquariums), please see the chart below (based actual ratios, NOT dosages):
Diagram for Alkaline and Acid Buffer mix in freshwater aquarium

*Please note that the above SUGGESTED Ratios are based on 100% pure water and in most instances the water used is not, especially if the Water is from a RO Filter that is not serviced regularly, or is simply a poor quality RO Filter (often one intended for human use, not aquarium use).
The bottom line is to start with these ratios, then adjust the rations until desired parameters are met; then write down these rations and use them in the future.

*As well as noted this is for low pH/softer water aquariums!!
For goldfish, livebearers, or even general community tanks, the use of Malawi Buffer (or Marine Buffer) is advised. Also the use of Acid Buffer as a counter buffer for equilibrium is generally not necessary.

*Do NOT use these ratios to adjust well, tap, blended, or established aquarium water!!
For this you need to add buffers as per aquarium parameters and then find a "Sweet Spot" where your aquarium maintains the desired parameters without a pH roller coaster. This often takes small doses until this is achieved.

*Finally these ratios are based on a starting measurement as per your tank size & suggested amount as per the buffer used (see your product instructions).
In other words if for your size aquarium 1 teaspoon is required of a certain buffer this becomes "1 Part" and then you would use 1/2 teaspoon if ".5 Part" of a counter buffer is also called for.

Adding Blended, RO, or RO/DI back to the Aquarium (Water Changes)

Once your KH, GH, pH, TDS, etc. are where you want these parameters, you water is reading for adding back to the main aquarium. A 32 gallon RubberMaid or similar trash can works for adjusting these parameters prior to addition after a water change (clean first with salt water before using).
If you are looking to have a flow through system, evaporation top off, or similar, I still suggest adjusting in this separate container, then pumping either slowly or quickly from this container.

I personally used two containers, one for simply filling slowly with RO water, then the next one is where I move this water to adjust and/or blend. I move the water to the second container when it is nearly empty, this way I have a constant filling of the first container while the second container is adjusted, then used.
This method still works well if the second barrel is used in a "constant slow water change". I would simply turn off the slow or demand pump while adjusting the water, then back on when complete (which should not take long).

Products that can aid in re-mineralizing RO water (many can be/should be used with other products for complete re-mineralization that includes carbonates)

Basic Electrolyte Replenishing Products (& Links):

*SeaChem Replenish;
Similar to Kent RO Right and API ElectroRight as a primary trace element/electrolyte replenishing product, although this product does add some buffers. Because of the mineral salts contained in this product, it is a good choice in particular for use in softer water aquariums as it does not as readily raise hardness. Replenish has very little affect on pH.
I recommend using this product to add to RO/DI water whether used in full or to "cut" tap/well water. Use the directed amount for the amount of RO or DI water used, not the full gallonage of the aquarium.

*Kent RO Right;
This is for basic trace elements, electrolytes, this product does NOT add most necessary buffers and most major minerals that are especially necessary for general freshwater fish tanks, especially livebearers, African Cichlids, and Goldfish.

*Aquarium Pharmaceuticals Electro Right;
As with Kent RO Right, this is for basic trace elements, electrolytes, this product does not add most necessary buffers and most major minerals that are especially necessary for general freshwater fish tanks, especially livebearers, African Cichlids, and Goldfish.

KH Buffers & GH/Mineral Additive Products (& Links):

*SeaChem Alkaline Buffer and SeaChem Acid Buffer
These to products above are for balanced carbonate/bicarbonates for correct KH & pH.
These are generally used for planted or low pH/soft water aquariums.

*SeaChem Malawi Buffer (or SeaChem Marine Buffer);
This would be the buffer of choice (used as directed) for Livebearers, Goldfish, African Cichlids, and similar higher pH/KH fish. I suggest using 1/2 the recommended amount in your RO water prior to addition to your aquarium then add to this until the desired KH is reached.

*SeaChem Cichlid Salt
Similar to SeaChem Buffer along with added sodium chloride salts

Wonder Shell for aquarium*Wonder Shells (Large) An important compliment mineral replenisher; mixes well with Electro Right, Replenish, RO Right, SeaChem Buffer or the similar but much less easy to use, SeaChem Equalibrium.
The Wonder Shell is an excellent compliment to follow up with Replenish or other initial RO Water Electrolyte additives, so as to constantly maintain essential mineral cations.
I recommend to use 1/4, 1/2, or a normal size Wonder Shell based on the type of aquarium kept & mineral needs. This goes for 100% RO/DI regenerated water, RO/DI cut water or 100% tap/well water.

*SeaChem Equilibrium;
Similar to Replenish, Wonder Shells or AragoMight, but with much more emphasis on Potassium and thus planted aquariums.
In most cases I have found this product NOT the better choice when compared to the use of Replenish along with 1/4 to 1/2 dose of Wonder Shells.
WHY? My extensive use of Equilibrium has not achieved as good of results, even in planted aquariums since it does not maintain the mineral Cations required in a closed system nor is it as useful for RO water use. AS WELL, in its use in certain conditions such as water softener water, it can occassionally percipitate out certain mineral Cations in a way that can cause a sudden fish die off.
I realize that that other professionals have a difference of opinion with me here, but I stand by my results and have always used & sold what I had the best results with, so while I really like SeaChem products and think this too is a good product, I have had better results using Wonder Shells, which is why I currently no longer sell this product.

These products can be used separately or together.
The API ElectroRight, Kent RO Right only adds important trace minerals and no carbonates and is usually inadequate by itself.
I generally would soak a Wonder Shell in RO water and then add Buffers (often both acid and alkaline for correct balance) or Cichlid or Marine Salt to further replenish major and minor elements as well as carbonates (as Wonders Shells have little carbonates).

Drinking Water/ Rain Water;

Also be real careful with water label “Drinking Water” (products such as Aquafina are simply RO water that has some minerals added for flavor for human consumption) as this is usually just RO water with a few minerals added for taste and does NOT have the electrolytes needed by fish. Usually pure spring water does have the proper electrolytes needed by fish.

I have seen many (especially on the internet) recommend rain water be used in place of tap water or similar, the reasoning is similar as with RO water that this water is more pure and therefore more healthy for the fish.
HOWEVER this reasoning is severely and dangerously flawed as rainwater generally has little or NO essential minerals for osmoregulation and as well as buffering capacity at all for maintaining a stable pH (rainwater tends towards the acid side on the pH scale) which will result in a rollercoaster pH in the aquarium.
Please note that the pH scale is logarithmic meaning a 1 point change up or down is equal to a tenfold increase in acidity/alkalinity.
Reference: Aquarium Chemistry; pH

Softened Water; Home/Office Water Softeners Use:

Home (or office) water softeners that employ salt (either sodium chloride or potassium chloride) should NOT be used for supplying aquarium water, as these strip most important minerals all the while increasing sodium to very high and out of balance levels (sodium is only required in trace amounts for most fish). The sodium that is present continues to strip ESSENTIAL calcium and other mineral ions. Running an RO system after a home water softener will not solve the problem of these odium ions.
This can severely affect osmoregulation in fish, especially many fish such as Loaches that normally prefer more soft water.
However these same softwater fish do not prefer soft water containing an unbalanced mineral content that is high in sodium but missing other essential mineral ions, which water from a home softener would be, regardless of whether you add back minerals such as the use of a Wonder shell or not!

The use of soft water from sources that utilize sodium OR EVEN from aquarium conditioners that have sodium bases is that the sodium often drives out the essential mineral cations.
The proof is the ability to maintain a good KH, however an un-naturally low GH often results.
One such test I conducted showed a KH of 200 ppm while the GH was only 20 ppm.

A review of Aquarium Water Conditioners:
Aquarium Conditioners, Information

The result is nearly NON-existent ESSENTIAL calcium, magnesium, and other positive mineral ions.
This can have severe affects on all fish, but is an ESPECIALLY noteworthy problem in Goldfish, Livebearers, and Rift Lake Cichlids!!

AS WELL, the use of Softened Water in certain conditions, such as some instances of combing with SeaChem Equilibrium, use of softened water will percipitate out certain mineral Cations in a way that can cause a sudden fish die off.

Another aspect is that softened water contains enough sodium to actually irritate a fish' epidermis, which in particular is harsh for scaleless or smooth scale fish (such as Loaches, many Catfish, Eels, Elephant Nose, and Ghost Knife Fish).

Although likely obvious to most saltwater aquarium keepers, the use of water softener water should NEVER be used for mixing saltwater or topping off a marine aquarium for evaporation.

See also:
Tap water for my Aquarium or Pond; Sodium

Here is how a home or office water softener works:
When the resin becomes saturated with calcium and magnesium, it is regenerated by passing an NaCl or KCl brine solution through the resin. The high concentration of sodium ions in the brine causes the reaction to be reversed with sodium (or potassium if KCl is used) replacing the calcium and magnesium ions which are then discharged into the waste water.

This sodium or potassium that is used to drive out mineral Cations of calcium and magnesium remain in the water, even if in small amounts. These sodium ions are enough to continue to drive out a considerable amount of essential mineral Cations so that simply adding these back via SeaChem/AAP Replenish, AAP Wonder Shells, etc. results in precipitation of these essential electrolytes.
Simple tests with an AAP Wonder Shell bear this out as the Wonder shells dissolves in a pile of dust, but never actually changes the water chemistry!

Here is the equation/formula:

Water Softener Reaction formula, equation


Necessary Minerals

From Original Article:
Do Fish Drink; Osmoregulation in Fish

Here are a few necessary TRACE elements/minerals (electrolytes) and their function.

For a related post that deals with trace elements:
“Plaster in Paris in Aquariums and Ponds”

It is important to have a proper Redox Potential which describes the ability for the loss of an electron by a molecule, atom or ion to the gain of an electron by another molecule, atom or ion.
Without this reducing Redox Potential many minerals cannot be absorbed and properly assimilated. So it is very important to keep a “positively charged” aquarium or a Balanced Redox Potential via proper dissolved oxygen levels, calcium and other electrolytes, proper cleaning procedures and water changes (UV Sterilization can help too).

For more information about the Redox Potential, please see this article:
*The Redox Potential in Aquariums (& Ponds) and how it relates to proper aquatic health (AVOID scam articles on the subject of Aquarium Redox such as by Aquariumscience that are only attack pieces and have no basis in practical experience)

For further reading on this subject, here are a few articles I recommend:

This other Aquarium Answers article is an excellent compliment:
Tap water for my Aquarium or Pond? From Chlorine and Chloramines to Phosphates & TDS

For more aquarium information, please visit this site:

*Sodium Ions:

Carl Strohmeyer- Copyright 2023

Other Recommended Reference & Product Sites

Aquarium Information
Aquarium Information and Resources (Pond too)

Fish Diseases, How to Treat Sick Fish
Fish Diseases | How to Treat Sick Fish

Premium Tropic Marin Pro Reef Sea Salt from Germany

Premium Tropic Marin Pro Reef Sea Salt from Germany

There is simply NO BETTER Reef Sea Salt (marine fish too)

*UV Sterilization, Sterilizer Use
The above article is the most in depth and constantly researched/updated article to be found ANYWHERE on the Internet!

TMC Total Dissolved Solids Monitor

An excellent stand alone product for testing your TDS from Tap, well, or even aquarium water.
A must have for any advanced aquarium keeper.

*Ich; Lifecycle, Identification, Treatment, Prevention

Authorized Seller of Aquaray Lighting

AAP AquaRay Ultra Premium Aquarium LED Lights
Highest in PUR, The ONLY LED with an IP67 rating or higher for water proofing along with a full 5 year warranty to back them up!
Why purchase brands without this rating such as the Finnex, Current, or Fluval only to be essentially placing an electronic light emitting device over your humid aquarium with little or no guarantee? In the long term, you WILL PAT MORE!

*Pond Care Information

*Aquarium Forum; Everything Aquatic & Aquarium Forum Board

*Fish as Pets Aquarium NewsFISH AS PETS
Fish as Pets contains articles and commentary of Interest to the Aquarium Hobby

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Aquarium Water Conditioners; Review, Information

By Carl Strohmeyer-PAMR 40+ years experience
Updated 8/3023

AQUARIUM (& Pond) WATER CONDITIONERS; their ingredients (where available), what chemical functions they perform and uses based on my opinions of each based on using these products in a professional capacity (35 years of aquarium maintenance and research).
Here are a few aquatic conditioners discussed:


The basic premise of an aquarium (or pond) water conditioner is to remove chlorine from tap water via Redox Reduction.
The most common active ingredient is sodium thiosulfate, however other similar sulfate based reducers or combinations there of are also used, especially in more advanced water conditions. This is why many have a subtle “rotten egg” sulfur smell.
As well, there are many other reducers that can break down chlorine including Vitamin C (albeit generally not always as rapidly at safe doses, reference Tap Water in Aquarium/Pond; Vitamin C Use). Even UVC energy from a True UV Sterilizer will slowly break down chlorine.

Being a reducer and chlorine oxidizer, the chemical reaction is essentially instant (see the experiment a few paragraphs down in the article).
As noted, most aquarium/pond water conditioners use sulfates such as sodium thiosulfate. Thiosulfate is a Redox reducing agent. It is routinely used as a titrant to determine concentrations of oxidants such as hypochlorite in bleach and dissolved oxygen in water.
It INSTANTLY dechlorinates water via this Redox reaction (producing new compounds including H2O), it does NOT alter the chlorine as is done in changing ammonia ions (NH3) to non toxic ammonium (NH4)

This allows for addition of water “de-chlorinated” by these products immediately to the aquarium or a water conditioner can be added in small increments while filling an aquarium via a hose or Lees Vacuum/Python type aquarium cleaning device/equipment.

Further References:
*Aquarium Redox; The only experience based article on this subject! (avoid article on this subject as it makes attacks based on opinions, not research and true experience)
*Aquarium Cleaning, Reasons, Methods, Devices, Equipment
*What is thiosulfate ion, and what is it used for?

It is worth noting that although the use of many water conditioners whether Prime, Start Right, Novaqua, or similar is usually after water changes to remove chemicals such as Chlorine; many (not all though) also either naturally stimulate fish slime coats (by adding electrolytes) or add ingredients for slime coat “bandages” and are useful for even very small water changes (such as 10%) even if the amount of chlorine added usually will not cause a problem in a healthy established aquarium.
The reason I say this is that is even small water changes can add some stress to fish and the addition of even full doses to small water changes can aid in adding electrolytes AND short term Redox reduction as well.

Much more about: Importance of Aquarium Redox

If your water company uses chloramines (which is common in the Southwestern USA), be aware of this and perform only 20% or smaller water changes in an established aquarium as the bio filter will generally remove the ammonia safely.
However for larger water changes or newer less established bio filters, I recommend using products such as Prime or Amquel Plus to remove the chlorine AND neutralize the ammonia/nitrites leaving these molecules still bio available for the nitrifying bacteria.

Recommended Product: SeaChem Prime Water Conditioner

Please note that the older Amquel or Ammo-Lock also neutralizes the ammonia, however these formulas do NOT leave it readily bio available for the nitrifying bacteria. Amquel or Ammo-Lock are OK for established aquariums; I just do not recommend using them for new less established aquariums or for aquariums that have been treated with medications.

Another important point about aquarium water conditioners is that many basic water conditioners such as API Tap Water Conditioner, Start Right, and even slime coat additive conditioners such as Novaqua and Stress Coat will remove chlorine and break the chlorine/ammonia bond in chloramines removing the chlorine, however leaving the ammonia ions behind.

How Much Water Conditioner to Use?
Often many manufacturers will suggest a dose equal to the entire tank water volume while another might suggest a dose amount equal only to the amount of water changed.
Which is correct?

The simple answer is both are correct.

Generally with an established aquarium, just using the amount of water conditioner as per the the volume of water changed is all that is needed.
However, since most water conditioners are Redox Reducers and help with natural slime coat production, if your fish are stressed, sick, or the tank is new, it might be best to use a dose equal to the entire aquarium water volume.
So this said, my general recommendation is to use a good water conditioner such as AAP ResQ or Prime at full dose, after ALL water changes, even if RO or DI water is used if only for the Redox and slime coat benefits.

Finally; Since most all aquarium/pond water conditioners are redox reducers designed to neutralize chlorine, a redox oxidizer; the use of any of these water conditioners after introduction of a strong oxidizer such as Potassium Permanganate will immediately neutralize this product.

Here is a little experiment I use to check the effectiveness of water conditioners;
Add Potassium Permanganate at double strength solution (according to manufacturers instructions) to a container of water, then add your water conditioner at recommended dose; the purple color of the Potassium Permanganate should immediately disappear indicating the effectiveness of your water conditioner and demonstrating how quickly it can remove chlorine (chlorine is an oxidizer like Potassium Permanganate, while the water conditioner is a reducer often containing Sodium Thiosulfate).

For more about Chemical Treatments, including Potassium Permanganate:
Aquarium Medications, Chemical Treatments

Some chemical dyes such as Malachite Green or Methylene Blue can also be neutralized by Prime, Amquel Plus or related water conditioners, however these are not the strong oxidizers that Potassium Permanganate is.
In experiments, it takes more than four times the dose of Prime to even moderately change the color of Malachite Green in a test solution, unlike the small amount needed to neutralize Potassium Permanganate.

This same experiment found that Prime and other water conditioners "neutralizing activities" do not last long once introduced into water.
So adding Prime, Amquel Plus, etc. then waiting for 15 minutes before adding Malachite Green, etc. yields no changes in the malachite green in solution.

It is also noteworthy that since these products are generally Redox Reducers, these products can temporarily lower available oxygen in the water. This is never a problem in an aquarium with even reasonably good water movement or aeration, HOWEVER if overused in a bowl with no circulation, this can deprive the fish of oxygen.

Please note that this article is an incomplete list of several popular water conditioners (and is only aimed at commercial water conditioners), not other alternative methods) and by incomplete I do not mean inaccurate information, I just mean there are many conditioners I did not review here (both good, bad or in-between).

For a companion article dealing more specifically with Tap water and hazards possibly there in: Tap water for my Aquarium or Pond? From Chlorine and Chloramines to Phosphates, Sodium, & TDS


Stress Coat


Stress Coat contains a special non-toxic polymer that is attracted to the skin of the fish forming a synthetic slime coat envelope
. Stress Coat also contains sodium thiosulfate, electrolytes such as sodium and sulfides which help reduce loss of electrolytes through the skin, gills, and damaged tissue. The Aloe Vera in STRESS COAT may inflammation of damaged fish tissue.

One major negative of Stress Coat is that it uses amine based polymers (see summary below) that have potential toxicity issues when used with Resins such as Purigen.

The effectiveness of Aloe Vera has been proven by independent studies conducted at the University of Georgia, School of Veterinary Medicine IF it can get to the fish.
It should be noted that testing has shown that Stress Coat is only effective in direct application where by the "blob" of slime/aloe lands directly on the fish.

Stress Coat in no way harms aquarium fish, alters pH, or affects the biological filter. No ammonia or nitrite was detected in the test aquariums. The results indicated that the Stress Coat formula reduced the wound size compared to untreated fish tissue. Aloe Vera is high in mucopolysaccharides, an essential component of many tissues and believed to help in the healing process.

An effective water conditioner for the removal of chlorine, breaking of the chlorine/ ammonia bond (in water containing chloramines) and adding an aloe slime coat.

This is a popular "discounter" slime coat treatment for direct application to a fish that is wounded from transport or other reasons. Albeit, application in the water has proven to much less effective from my experience & testing as it tends to just "blob" on the aquarium bottom and not get aught up in the water column.
MOREOVER, I have found it less effective for overall slime coat generation after a water change.
For this and general water application, AAP Res-Q, Quinex, & Shieldex as well as AAP/SeaChem StressGuard are vastly superior products as these do not rely on the actual "slime" and aloe to reach the fish to be effective, rather it instantly creates a Redox reducing environment in the water and on the epidermis of the fish itself.
As well, both the "slime" part of Res-Q & Sheildex mix much better with water and if direct application of slime coat after an injury is indeed needed, AAP Res-Q is by far the better and more effective choice from my experience.

Interestingly some "less informed" aquarium stores use Stress Coat to squirt into the fish bag as a fish stress reducer.
Unfortunately, my own tests and use has shown this practice does little other than aid somewhat in lowering Redox oxidizers in the water.
Most informed professionals have long employed a drop of MethyBlu as well as AAP Res-Q into the bag to lower stress and prevent disease transfer.
A new product, StressGuard can also be used as a substitute for Stress Coat (I should note that Res-Q disappeared from the market for over a decade, but AAP Professional Treatments has brought back this water conditioner that was part of most aquarium professionals arsenal for some time).

Ingredients are safe for both fresh and saltwater.


AAP Res-Q Medicated Aquarium Water Conditioner

AAP Res-Q is a product originally created by Aquatronics that has been brought back by AAP Professional Treatments (beware of clearance product sold elsewhere as AAP is the ONLY seller of this product online).
This is THE PREMIER freshwater conditioner used by professionals and should be part of ANY SERIOUS aquarium keepers inventory. IN FACT this was the aquarium water conditioner I used by far the most (even over the now popular Prime). WHY? Because results showed it to be most effective in most scenarios calling for a water conditioner. AAP Shieldex was my 2nd choice and 1st choice for marine aquariums followed by Prime as my 3rd most used water conditioner (which has scenarios where it might be the best choice)

AAP/Aquatronics Res-Q is an excellent choice for a water conditioner when fish have frayed fins or have visible abuse.
AAP Res-Q is a most effective product with seven way action; RES-Q detoxifies and conditions water by polymeric complexing (bonding) of metallic ions.
REs-Q then coats the fish with a slippery medicated bandage of Quinine Hydrochloride, Sulfamethazine, n Alkyl dimethly Benzyl Ammonium Chloride, & Propyl Paraben.
Res-Q also balances osmotic processes, removes chlorine, clarifies water and aids in safe shipment of fish. Res-Q does not color the water with its use.

Great when used in conjunction of a Medicated Wonder Shell

The key ingredients that separate Res-Q from all other water conditioners are:
-Quinine Hydrochloride; An anti external parasitic (including Ich)
-Sulfamethazine; An anti microbial (think Triple Sulfa)
-n Alkyl dimethly Benzyl Ammonium Chloride; A phase-transfer catalysis, an important technology in the synthesis of anti-microbials which allows the other medications to better adhere to the fish epidermis

Used in lieu of other water conditioners, especially if medication on the fish is indicated such as after injury or introduction of new fish.
As well squirting Res-Q directly on a fish after a medicated bath or when introducing to the aquarium is another recommended use for this water conditioner

NOTE: my regular everyday use of Res-Q in my 1000s of client aquariums (in particular the 110 tanks at the Bahooka Restaurant) showed lower incidence of disease when used as the primary water conditioner where applicable as compared to ALL OTHERS including the popular SeaChem Prime!
Speaking of Prime, Res-Q can be combined with Prime (both at normal dose) when there is a need for chloromine removal and de-toxification of ammonia is also called for.

Where to get:
*AAP Res-Q
*AAP Quinex; Slime Coat Medicated Treatment/Conditioner
*AAP Medicated Wonder Shell

aquarium water conditioner, stress reliever, slime coat regeneration, StressGuard


SeaChem StressGuard by AAP is a better alternative to Novaqua and especially API Stress Coat.
While the comparisons are not exactly "apples to apples" when compared to the before mentioned other similar water conditioners, if stress and injury are the reason for use, StressGuard is the vastly superior product.

APP/SeaChem StressGuard does NOT remove chlorine as would Stress Coat or Novaqua, however it is still a Redox Reducer based on the aldehydes contained there in.
Where StressGuard excels over these others is that while Aloe Vera is certainly a proven ingredient, most rarely gets on the fish in normal aquarium application while the protein active colloids found in StressGuard immediately disperse into the aquarium (or pond) water column and are much more effective in healing of the fish' epidermis.

Unlike others, AAP StressGuard lowers ammonia toxicity similar to Methylene Blue, but without the affect on the bio-filter use of Methylene Blue would have in a main display aquarium.
As well StressGuard is pH neutral, unlike Novaqua in particular which can lower pH. StressGuard does not affect CO2 readings in planted aquariums, unlike Novaqua.

As a caution though, StressGuard should not be used with aquarium remedies that include copper such as Cupramine or Medicated Wonder Shells. HOWEVER, Regular AAP Wonder Shells work well with StressGuard and in fact work synergistically/complimentary together, so I recommend BOTH used in instances of fish stress.

For use with new fish, suspected ammonia/nitrite toxicity, minor to moderate torn fins, injury or similar, use in main holding or hospital tank especially after "Fish Bath", and use with many antibiotic treatments to ease stress (may reduce chemical treatments such as Malachite Green, so use not advised).

Where to get:
*Seachem StressGuard
*Regular Wonder Shells from AAP


Ammo-lock contains sodium thiosulfate pentahydrate. Ammo-lock works in both fresh and saltwater, to detoxify ammonia and remove chlorine and chloramines. Ammo Lock "locks" up ammonia in a non-toxic form (ammonium) until it can be broken down by the tank's natural biological filter and/or used by plants.
However AmmoLock creates acidic by-products that decrease the pH. As well, ammo-lock does not bind ammonia in a way to have it available for your filters to use

For the removal of chorine and chloramines.
This product is useful for the detoxification of ammonia, generally in established aquariums. I usually only use this product when the aquarium is well established and ammonia (NH3) is high for reasons such as a dead fish that was not removed quickly (please note, most ammonia test kits will still show ammonia present in the form of NH4 after using this product) or in areas where chloramines are used.
Ingredients are safe for both fresh and saltwater.

This is not my first choice for ammonia removal, ESPECIALLY in tanks that are still cycling (Prime is much better here). One reason, as noted earlier, is continued use of Ammo-Lock can cause cessation of the nitrogen cycle since it does not readily allow for bio availability of ammonia to nitrifying bacteria.

aquarium water conditioner, electrolyte stimulant


Start Right contains allantoin (5-Ureidohydantion; Glyoxldiureide 2, 5 - Dioxo - 4 imidzolidinyle – urea) which is used in humans for the treatment of: skin ulcers, wound, scalds, burns and sunburns, carbuncles, acne and skin eruptions, fissures and abrasions, impetigo, eczema, psoriasis. This is a naturally occurring chemical even found in earthworms.
Start Right is a multi-beneficial water conditioner that removes chlorine and chloramine, neutralizes heavy metals, aids in cell regeneration and in the additional production of the fish’s natural slime coat, adds beneficial. It also contains chlorides of sodium and potassium, and polyvinylpyrrolidone which helps reduce loss of electrolytes through the skin, gills, and damaged tissue.
It is a complete water conditioner that stimulates the natural secretion of slime to protect fish from the harmful effects of handling, shipping, fish fighting and other forms of stress.
Start Right removes chlorine and chloramine instantly, neutralizes heavy metals, adds beneficial electrolytes and guards against secondary infection.

For the removal of chlorine, breaking of the chlorine/ ammonia bond (in water containing chloramines), adding of electrolytes for stress, and the natural generation a slime coat.
This is probably my favorite basic overall water conditioner for established aquariums (I use this along with SeaChem Prime).
Start Right will not remove ammonia or interfere with plant growth by removing nitrogenous compounds needed by plants. This product is also very economical.
Ingredients are safe for both fresh and saltwater.

Where to purchase: *Jungle Start Right

aquarium water conditioner, electrolyte, ammonia remover


Prime contains complexed hydrosulfite salts which removes chlorine, chloramine and ammonia. Prime also converts ammonia into a safe, non-toxic form (ammonium) that is readily removed by the tank’s nitrifying bacteria.
Prime may be used during tank cycling to alleviate ammonia/nitrite toxicity.

How Prime Converts toxic ammonia (NH3) to non toxic ammonium (NH4):
The process that takes place between Prime and toxic ammonia is not a straight conversion from NH3 to NH4.
Prime contains a binding agent that works to temporarily convert toxic ammonia (NH3) into a non toxic imidium salt using complexed hydrosulfite salts to chemically convert the ions in ammonia into a non toxic imidium salt.
It is noteworthy that this is a temporary conversion and Prime will only bind the ammonia in this form for up to 48 hours before the ions are free to re-associate into toxic NH3.

Prime also detoxifies nitrite and nitrate, allowing nitrifying and denitrifying bacteria to more efficiently remove them. It will also detoxify any heavy metals found in the tap water at typical concentration levels.

The ingredients of Prime also promote the production and regeneration of the natural slime coat and are non-acidic and will not impact pH.

While Safe is a similar dry version of Prime, with the exception that it does not detoxify heavy metals, nor will it stimulate the natural slime coat of the fish. Unfortunately, due to its dry state, those benefits can not be achieved. Safe cannot be made into Prime, as it does not have stabilizers like Prime and will not last long term in a liquid form. If diluted into a liquid, it must be used immediately.
For these reasons, for the average aquarium keeper, I generally recommend Prime over Safe.
Reference: AAP/SeaChem Safe

For removal of chlorine, chloramines, and the de-toxifying of ammonia, nitrites and nitrates. This product adds electrolytes that aid in natural slime coat generation and proper osmotic function which generally all this needed for fish stress.
This is my favorite conditioner to use in newer aquariums, aquariums with high ammonia, for water changes in tanks under medication treatment, or for use in areas where chloramines are in tap water. One reason I like this product is that is does what it claims!
Prime is also a great product to use if high ammonia or nitrites are encountered during cycling of a new aquarium while fish are present, as this product will NOT interfere with the important Autotrophic nitrifying aerobic bacteria (as my own studies as well as lab studies have shown).

Please note that fishless cycling is best, please read this article:
Aquarium Nitrogen Cycle; Methods for Cycling

Please note that when using Prime/Safe (and Amquel Plus) for neutralizing toxic ammonia (NH3) that these products work basically "instantly" by converting toxic ammonia ions into non toxic bio available ammonium (NH4) ions.
There is no residual effect, so new toxic NH3 will begin to accumulate after addition of Prime (or Amquel Plus) and the water change, however generally if you are carefully feeding and keeping the bio load as low as possible this should be adequate if water is changed and Prime is added every other day (until the high ammonia "Crisis" is over).

SeaChem Prime works for ammonia detoxifying by containing a binder which renders ammonia, nitrite, and nitrate non-toxic.
As noted at the beginning of this article, most dechlorinators operate through a chemical process known as reduction. In this process, toxic dissolved chlorine gas (Cl2) is converted into non-toxic chloride ions (Cl-). The reduction process also breaks the bonds between chlorine and nitrogen atoms in the chloramine molecule (NH2Cl), freeing the chlorine atoms and replacing them with hydrogen (H) to create ammonia (NH3).

Where to get SeaChem Prime/Safe:
SeaChem Prime; Complete Water Conditioner
SeaChem Safe; Syper Concentrated Complete Water Conditioner
Safe is an excellent alternative for ponds or large aquarium systems. While Prime is a concentrated conditioner, Safe, being dry is even much more concentrated (1 kg. treats 240,00 gallons or 960,000 liters)

Typically, other water conditioners (dechlorinators) stop there, leaving an aquarium full of toxic ammonia! Seachem Prime goes one more step by including an ammonia binder to detoxify the ammonia produced in the reduction process.

Ingredients are safe for both fresh and saltwater.
For further information about this product, please read this FAQ article:
Prime FAQs

API Tap Water Conditioner


This is a very basic aquarium and pond water conditioner that is sometimes all an aquarium or pond owner needs to use.
This product contains Sodium Thiosulfate and nothing more which is a basic yet effective chlorine remover and Redox Reducer which make this product a popular and cost effective aquatic conditioner.

“Tap Water Conditioner” does not remove chloramines, however it breaks the chlorine/ammonia bond releasing the ammonia ions, so this product should not be used with larger water changes over 20% in all but the healthiest most established of nitrifying filters in ones pond or aquarium, however if chlorine is all your water company uses, “no worries”.
This product also does not aid with the addition electrolytes like other somewhat less basic conditioners such as “Start Right” nor does it aid with either natural slime coat or add a synthetic slime coat like many other water conditioners.


Weco DeChlor, Aquarium Chlorine RemoverA similar product to API Tapwater Conditioner.
DeChlor also contains Sodium Thiosulfate and nothing more. This too is a basic yet effective chlorine remover and Redox Reducer.

The big advantage for this product is the price, as it is an effective chlorine remover and chloramine ammonia/chlorine bond "breaker", YET is costs less than any other product on the market.
Weco, who makes this product is not the large company most others are such as API, rather a small company out of Long Beach CA. that uses the same simple labels they have for 5 plus decades of popular local aquarium hobbyist use.

For basic economical removal of chlorine in aquariums and ponds (this product is available in 32 oz pond use sizes)


AAP Shieldex Slime Coat Aquarium Water ConditionerAAP Shieldex is a product originally created by Aquatronics that has been brought back by AAP.

AAP Professional Treatments "Shieldex" is an excellent choice for a water conditioner when fish need an additional boost to their slime coat.
I have professionally used this product & similar products in large quantities in my 1000+ aquarium maintenance business. AAP Shieldex is far superior to StressCoat, for one it allows for more natural slime generation and does not tend to "blob" on the bottom of the tank.
AAP Shieldex is a Vitamin E fortified protective, stress relief and disease preventing slime coat treatment for ALL fish (safe for all fish; freshwater, saltwater, invertebrates).
Next to Res-Q and followed by Prime, this was one of my "Go to" water conditioners and one that my 1000s of observations bore out to to be better than most.

Ingredients: Polyvinylpyrrolidone, Polyacrylamide, Propyl Paraben, Sodium Thiosulfate, Vitamin E

* AAP Shieldex has a specific use when setting up a new tank. Nitrifying bacteria enjoy clinging to the slime coat it produces. Success in cycling tanks has been achieved by squirting the liquid directly into the filter bed prior to adding water.
* Shieldex can be used for heavy metal detoxification.
* Shieldex is one of the finest water conditioners to remove toxic elements and place a slime shield on fish. Compare quality/slipperiness and concentration with other products.

Where to get:
*AAP Shieldex


AAP Proaqua Aquarium Water Conditioner, Heavy metal removerAAP ProAqua is a product originally created by Aquatronics that has been brought back by AAP Professional Treatments. This has been an aquarium professionals go to product for water conditioner when heavy metals are present and/or instant aging of the water is required (in particular, often in Amazon River biotope aquariums).
I personally was never without this product in my aquarium maintenance kit, as while it was not my regular go to water conditioner for most of my clients aquariums, when a situation called for this product, there was and still is NOTHING similar in the market place!

AAP ProAqua is a very unique water conditioner as it removes metal ions, including iron & zinc. As well, ProAqua removes chlorine.
Safe for ALL fish and invertebrates both marine and freshwater

Where to get:
*AAP ProAqua

aquarium water conditioner, electrolyte, ammonia remover


The formula of NovAqua is proprietary, so not all ingredients are available.
It is assumed that Novaqua contains sodium thiosulfate (a common Redox Reducer) and Edetates.
Novaqua also contains phosphates for buffering to stabilize water after water changes (often when water is added from the tap it immediately picks up O2 and CO2 and is unstable in pH, this aspect of Novaqua helps here).
The phosphate buffer system of Novaqua produces a 5 mg/L of phosphates in the aquarium as compared to the 30 mg/L shown in labs tests to grow algae.

NovAqua also contains electrolytes; cations (Positively charged atoms or molecules) and anions (negatively charged atoms or molecules) that are required by freshwater fishes. Freshwater fishes remove these ions from water via the gills. The need by fish for these ions is increased during times of stress.

The original conditioner that adds a slime coat, adds electrolytes buffers water, and removes chlorines.
NovAqua is useful for use water changes where buffering is needed due to pH changes after water changes. The level of phosphates used for buffering are not usually a problem for most aquariums, however if you already have high phosphates or algae problems I would avoid this product.
I also do not recommend the use of Novaqua in planted aquariums where added CO2 is utilized as this may affect your CO2 readings.
Otherwise this is an excellent product when one desires a conditioner that adds a slime coat and buffers a well.
Ingredients are safe for both fresh and saltwater.


The active ingredient in Amquel is hydroxymethanesulfonic acid, sodium and salt. Amquel converts ammonia to a non-toxic form (ammonium) until it can be broken down by the tank's natural biological filter and/or used by plants.
Amquel works by virtue of the hydroxymethane- end of the molecule reacts with ammonia to form a non-toxic, stable water-soluble substance which is acted upon by the bacteria in biological filtration.

This reaction effectively removes the toxic ammonia from solution. Even in water of low pH (under 7.0) the above reaction proceeds to completion.
This is because even at pHs below 7.0 there is always some "free" ammonia (NH3) and the AmQuel will scavenge it from the water. This is why AmQuel works faster at higher pHs and in saline waters.

One of the first products for chloramine and ammonia removal. It is very effective in binding the ammonia (NH3) where that it stays non toxic even when nitrifying bacteria are not fully active.
Although safe for saltwater, I have seen this product lower pH, for this reason it is not my first choice in this type of conditioner (Prime is my favorite as stated earlier).

Tetra AquaSafe Aquarium Water Conditioner


The active ingredients in Aqua safe are Sodium hydroxymethane, sulfinate, polyvinvy. proxllidones, organic hydrocolloids, and organic chelating compounds.

This product removes Chlorine, breaks the bond of chlorine and ammonia in chloramines (however it does NOT neutralize the ammonia), it also has several key ingredients for natural slime coat stimulation and electrolyte balance.
This is a good product where chloramines or ammonia are not a problem (I would prefer Prime for a new tank, recently medicated tank, or in areas where tap water contains chloramines).

For established tanks this is excellent and I prefer the natural slime coat protection it provides for a healthy established aquarium.

The "Plus" version includes biopolymers to support health. New vitamin and mineral blend including: vitamin B complex for health, Iodine and Magnesium for activity.

Amquel plus


Since this is a relatively new product, the ingredients are proprietary to Kordon and not yet disclosed.

AmQuel+ (also known as AmQuel Plus) is a recent chemical invention that has the ability to make the "Nitrogen Cycle" (involving ammonium/ammonia/nitrites/nitrates) totally nontoxic in aquarium and pond keeping, without interfering with its process in any way, and without interfering with the beneficial bacteria that are involved with the cycle (as with SeaChem Prime).
Further, AmQuel+ detoxifies/removes all of the toxic nitrogen compounds that can appear in aquarium and pond water over time.
As with Prime, I highly recommend this product for aquariums that are still not fully cycled in that it does NOT interfere with nitrifying bacteria (cycling), which is very important and a major selling point for this product!

A new product without a lot of practical experience (including by me, although others I trust have been using this more and more with good results that hold up manufacturer claims). The claims by Kordon sound very promising, and this may turn out to be an excellent product for new aquariums in particular, although use in established aquariums seems unnecessary.
Ingredients are safe for both fresh and saltwater.


Novaqua + is a newer product and again has proprietary ingredients that the company will not totally divulge. NovAqua+ claims to provide, in a single product, everything necessary to handle all of the needs when treating tap water for aquatic life, except for handling nitrogen compound removal such as ammonia, nitrites, nitrates which requires Prime or Amquel Plus (which either product is compatible with Novaqua Plus).

NovAqua+ is the newest generation of NovAqua, it is the latest stage of technological development by Kordon in water conditioners for aquariums and ponds
As with regular Novaqua, NovAqua Plus provides multiple protective colloid coatings on the fish's body to replace or reinforce the natural slime coating that is essential to counteract injury, infection, and adverse environmental exposure.

These organic polymers effectively shield wounds on fish, prevent the loss of internal fluids and electrolytes, and protect fish from external toxins and pathogens.
NovAqua Plus similarly buffers water like regular Novaqua

NovAqua Plus contains Echinacea and vitamins that are soluble in water and absorbed by fishes and invertebrates; the vitamins used in NovAqua+ are capable of boosting disease-resisting immune functions, healing open wounds and sores, slowing the spread of infection, and promoting cellular

Again a new product without a lot of practical experience (including by me). If this product lives up to claims such as aiding in osmotic function as well as chlorine removal and heavy metal removal, this may be a very useful product as well. Due to claims of iodine removal, I would not recommend use in marine reef tanks (as many soft corals need iodine)
Ingredients are safe for freshwater.


Tetra Easy Balance makes these claims:
Increases Carbonate Hardness; The appropriate amount of carbonate hardness is added to the aquarium water compensating for KH losses, which occur as a result of nitrification.
Stabilizes the pH value on a sufficiently high level, preventing a drop to biologically harmful levels (pH crash) and produces a certain amount of CO2 preventing excessive pH values.
Phosphate Removing Effect – In a standard aquarium (30gal) the phosphate concentration is reduced to zero during most of the 6-month period.

Nitrate Reduction with Nitraban™ – Serves as a nutrient for denitrifying bacteria that consume the oxygen releasing nitrogen from the aqua. however this assumes that your aquarium has a healthy anaerobic nitrate reducing filter, which most freshwater aquariums generally do not.
Tetra Easy Balance is a popular water conditioner in some aquatic circles, mostly in Europe.

I have also researched the ingredients which leaves me with even more questions (especially since results seem to be mixed at best).
One of the major problems with Tetra Easy Balance is its sodium based base.
This makes this product work like a sodium based water softener driving out essential mineral cations necessary for osmoregulation, this often results in a too low GH unbalanced KH/GH and poor Redox Balance.

Reference: Fish Osmoregulation; Water Softener use.

Here are few major ingredients:
*Sodium Hydroxide (up to) 2.5% (a base)
*Tartaric Acid (up to) 2.5% (an acid)
*Formaldehyde (up to) 2.5% (a Redox Reducer).

Based on these ingredients, some of the claims can hold up but others cannot.
As well, I found GoldLenny’s comment here interesting:
“There is a forum thread that I read a while back about a guppy tank where the guppies did not breed or have babies even once during the time of the Easy Balance dosing on the tank.
IMO, anything that stops guppies from breeding has to be a serious chemical compound that can't be good for our fish. If Tetra was to re-market the product as a fish birth control and give full disclosure of the negatives of the product, then I may not have as many complaints about the product.”

Also this comment:
GoldLenny (Quote: “since Tetra will pretty much sell anything in a bottle... look at their Easy Balance with Nitraban product which is pure JUNK!!!”)

The bottom line is this is NOT a product I could EVER recommend!!
The problem with Guppies PROVES my concern as to this products effect on ESSENTIAL mineral cations and Redox Balance, which guppies are more sensitive to than some other fish.


This is an incomplete list that I will add to as time goes on and I will also update as new products and information becomes available.
Also it should be noted that most water conditioners of all types (basic, artificial slime coat replacer, and chloramine/ ammonia remover) have similar properties and ingredients and some of the outrageous claims I have read on the internet such as "Start Right is not safe for marine aquariums while Novaqua is" are without any scientific merit; if anything the phosphates in Novaqua can cause more problems than any ingredient in Start Right!

It also should be noted that ALL these types of chlorine/chloramine removing conditioners are Redox Reducers and thereby are helpful in maintaining a healthy aquatic environment by aiding in the removal oxidizing free radicals from the water (albeit temporary).
This why it is perfectly fine to add a full tank dose even if only 25% of the water is changed.
Reference: Aquarium Redox: Balance

Due to this reducing property of these products, you may also notice a slight to even moderate increase in cloudiness after use of these products due to the removal of oxidizers in the water, do not be alarmed this is perfectly normal and a healthy tank will clear in a few hours or less.

Please also note that some of the ingredients can expire with time especially when left in an unsealed container (sodium thiosulfate is a reducer and will be affected by air borne oxidizers). The time this will take will vary, although personally I would not use an open bottle after one year based on the degradation of sodium thiosulfate.

An interesting test I perform that shows the effectiveness of these products is to add potassium permanganate (which is an oxidizer like chlorine) to test water, then add your water conditioner at the recommended dose and watch the purple potassium permanganate color disappear instantly.

Note about amines used in many of these products:
“Amines are a class of organic compounds of nitrogen that may be considered as derived from ammonia (NH3) by replacing one or more of the hydrogen atoms by organic radicals, such as CH3 or C6H5, as in methylamine and aniline.
The former is a gas at ordinary temperature and pressure, but other amines are liquids or solids.
All amines are basic in nature and usually combine readily with hydrochloric or other strong acids to form salts.”

As per my professional recommendations for water conditioners, it is quite simple based on the 1000s of aquariums under my care as well as research;

*For an everyday water condition, "AAP Shieldex" is easily my choice and is second to none as per the main reasons to use a water conditioner and is superior as to slime coat restoration (vastly superior to API Stress Coat)

* If an aquarium has had or is having possible disease issues, or new fish have been added, AAP Res-Q is the clear choice. There is no competition to this product to even compare

*If ammonia, nitrites, nitrates, or chloramines are an issue, AAP/SeaChem Primes is your best choice

Finally, I have a good article about tap water that compliments this article and I recommend reading: "What I should know about Tap Water"

Other Recommended Reference/Product Sites

The article below is a MUST READ for anyone interested in moving from basic aquarium keeping to more advanced aquarium keeping, including better improved Redox Balance:
Aquarium, Pond UV Sterilization and affect on water conditioners
Aquarium & Pond 'TRUE' UV Sterilizer Use

Fish Diseases, How to Treat Sick Fish
Fish Diseases | How to Treat Sick Fish

Freshwater Aquarium Care
Freshwater Aquarium Care

Best Aquarium Lighting Information
Aquarium Light Information

This is THE article for in-depth, researched, and regularly updated information on the subject of aquarium lighting; a MUST READ!

Pond Care Help

Best UV Lamps, BulbsUV Replacement Lamps
For TRUE High Output, Hot Cathode, Low Pressure UVC Germicidal Bulbs, not the low output medium pressure bulbs commonly sold at Amazon or eBay

API Furan 2
API/AAP Furan 2 (Nitrofurazone)

One of the more effective treatments to use in fish medicated baths, from the leader in aquarium medication use information

Algone Aquarium Nitrate Control

Algone Nitrate Reducer

Algone is an excellent product to utilize to lower nitrates, as enzymes in Algone break down proteins, carbohydrates and metabolic waste into insoluble complex structures

Fish as Pets Aquarium News

Fish as Pets with articles & commentary of Interest to the Aquarium Hobby


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In Chronological order of writing with the newest at the top

  1. How to Treat Sick Fish
  2. Whirling Disease in Fish
  3. Reef Aquarium Chemistry Maintenance
  4. Use of RO, DI, Softwater in Aquariums
  5. Lighting Theory of a Planted Aquarium- RQE, PFY, PAS, & PUR
  6. Aquarium or Pond Bio Load
  7. Tuberculosis in Fish
  8. PUR vs PAR in Aquarium Lighting
  9. Head Pressure in Aquarium and Pond Water Pumps
  10. Fin/Tail Rot For Betta & ALL Fish
  11. Angelfish Virus/Aids
  12. Activated Carbon
  13. Fish Baths/Dips as an aid to treatment
  14. Streptococcus gram positive bacterium in aquariums, Eye Infections
  15. Hydrogen Sulfide
    production in anaerobic De-Nitrification for Aquarium/Ponds
  16. Fish Shipping
  17. Aquarium Size, Fish Stunting
  18. Aquarium Algae,
    BBA & Brown Algae in particular
  19. Aquarium Salt (Sodium chloride) in Freshwater Aquariums
  20. Betta Habitat; Wild Bettas to Domestic Betta environment parameters
  21. HITH; Hole in the Head Disease
  22. Aquarium Protein Skimmers, Ozonizers
  23. Power Head/ Water Pump Review
  24. Molly Disease/ Mollies in an Aquarium
  25. Basic Fish Anatomy, Fin Identification
  26. Aquarium Moving/ Power Failures
  27. Octopus as Aquarium Pets
  28. Aquarium Nitrates
  29. Ichthyophonus protists, fungus in fish
  30. Aquarium and Pond Filter Media
    Types; Mechanical, Bio, Chemical
  31. Aquarium Water Conditioners (also Pond)
  32. Fish Parasites; Trematodes & Monogeneans; Annelids and Nematodes;
    Flukes, internal worms, Detritus Worms (often confused with Planaria), Micro Worms
  33. Aquarium Silicone Application;
    DIY Aquarium Repair & Glass thickness
  34. Pond Veggie Filters; DIY Bog Filter
  35. The difference between Plaster of Paris and Aquarium Products such a Wonder Shells:
    Identification, prevention & Treatment
  37. AQUARIUM TEST KITS; Use & Importance
  38. SEXING FISH; Basics
  39. Chocolate Chip, Knobby and Fromia Starfish
  40. Freshwater Velvet & Costia
  41. Usnic Acid as a Fish Remedy
  42. Aquarium Heaters; Types, information
  43. The Lateral Line in Fish, Lateral Line Disease
    or Head and Lateral Line Erosion (HLLE)
  44. Tap Water use in Aquarium; Chloramines, Chlorine
  45. Can Black Ghost Knife fish give an electric shock?
  46. Bio Wheel Review; Do Bio-Wheels really work?
  47. How do Fish Drink?
    Use of RO Water
  48. Cyclops, and Predatory Damselfly larvae
  49. Betta with Dropsy;
    Treatment and Prevention of DROPSY in all fish
  50. pH and KH problems in African Cichlid Aquarium
  51. Aquarium Gravel, which size?
  52. Blue green algae, Cyanobacteria in Ponds/Aquariums

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*Sponge Filters that far outperform all other brands or DIY:
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UV Replacement Bulbs/Lamps Directory:
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*A CLEAR POND; Care & Information

Fish Food Information:

Aquarium & Pond UV Sterilizer Use Articles
-Unique articles such as unique UV ideas as well as dispelling myths

Directions/ Instructions/Downloads; Aquarium Pond Products

Aqua UV versus TMC UV Sterilizer
VIDEO: Aqua Pond UV vs TMC AAP Pond UV Clarifier Sterilizer

A comparison of the two top large pond/aquarium-system UV Sterilizers and why the AAP/TMC comes out as the best when price and dwell time is considered

Best Aquarium & Pond Medications
VIDEO: AAP Professional Aquarium & Pond Medications


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