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 (29 years of aquarium maintenance and research). Here are a few aquatic conditioners discussed: Stress Coat, Ammo Lock, Start Right, Prime, Novaqua, Amquel, Novaqua Plus, Amquel +, Tetra Aqua Safe.

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 Redox reduction as well (even though this aid is very short term).

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. If your water company uses chloramines (which is common in the Southwestern USA), be aware of this perform only 20% or smaller water changes in 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. Please note that the older Amquel or Ammo-Lok also neutralizes the ammonia, however these formulas do NOT leave it readily bio available for the nitrifying bacteria. These later products are fine for established aquariums; I just do not recommend using them for new less established aquariums.

This article is an incomplete list of several popular water conditioners and by incomplete I do not mean inaccurate information, I just mean there are many conditioners I did not review here.

Before I begin the list I would like to pass 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 (which is an oxidizer like Potassium Permanganate, while the water conditioner is a reducer often containing Sodium Thiosulfate).



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 helps reduce loss of electrolytes through the skin, gills, and damaged tissue. The Aloe Vera in STRESS COAT reduces 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, please see this article:
Water Conditioners That Contain Amines And Ion Exchange Resins

The effectiveness of Stress Coat with Aloe Vera has been proven by independent studies conducted at the University of Georgia, School of Veterinary Medicine. Researchers found that Stress Coat helped heal wounds and speed tissue re-growth. Dr John Gratzek summarizes the results: "Personally, I am satisfied with the results since my initial thoughts were skeptical to say the least. These definite statements can be made without equivocation: 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.

USE; 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 my favorite slime coat treatment for direct application to a fish that is wounded from transport or other reasons. I however have found it less effective for overall slime coat generation after a water change.
Ingredients are safe for both fresh and saltwater.

AMMO-LOCK;
Ammo-lock contains sodium thiosulfate pentahydrate. Ammo-lock works in both fresh and saltwater, to detoxify ammonia and remove chlorine and chloramines. 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.

USE: For the removal of chorine and chloramines. This product is useful for the detoxification of ammonia, especially in new aquariums. I usually only use this product when the aquarium is new, ammonia (NH3) is high (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 better here).



START RIGHT;
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. Removes chlorine and chloramine instantly, neutralizes heavy metals, adds beneficial electrolytes and guards against secondary infection.

USE:
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 the most), 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.



SEACHEM PRIME;
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. Prime 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 promotes the production and regeneration of the natural slime coat and are non-acidic and will not impact pH.

USE:
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. This is my favorite conditioner to use in newer aquariums, aquariums with high ammonia 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 (fishless cycling is best, please read this article: Aquarium Nitrogen Cycle), as this product will NOT interfere with nitrifying aerobic bacteria (as my own studies as well as lab studies have shown)
Ingredients are safe for both fresh and saltwater.
For further information about this product, please read this FAQ article: Prime FAQs


API TAPWATER 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 remove 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 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 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 coar like many other water conditioners.


NOVAQUA;
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.

USE:
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.

AMQUEL;
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 pH's and in saline waters.

USE: 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 (although use with Novaqua counters this), for this reason it is not my first choice in this type of conditioner (Prime is my favorite as stated earlier).
Ingredients are safe for both fresh and saltwater (when not over used).

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

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




AMQUEL +;
Since this is a new product, the ingredients are proprietary 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. Further, AmQuel+ detoxifies/removes all of the toxic nitrogen compounds that can appear in aquarium and pond water over time. This product is similar to Prime in that it does NOT interfere with nitrifying bacteria (cycling), which is very important and a major selling point for this product!

USE: 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.
For more information, please read this FAQ article: Amquel Plus


NOVAQUA +;
Novaqua + is a new 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). For the removal of toxic nitrogen compounds, Kordon recommends the use of AmQuel+

USE: 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.


CONCLUSION;
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 (especially in relation to Kordon’s new Amquel + and NovAqua +)
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; this why it is perfectly fine to add a full tank dose even if only 25% of the water is changed.
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:
"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."

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