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Fish Diseases | How to Treat Sick Fish

Sick Fish, How to Treat, cartoon  

By Carl Strohmeyer-PAMR 40+ years experience

Updated 5-9-23

Gill, How to treat sick fish, 1 The purpose of this article is not to provide any specific treatment regimen for the readers fish, rather to provide an outline that will provide a better chance for success over the typical "my fish are sick and what medications & how much should I dump into my aquarium" question.
Obviously the starting place is aquarium disease prevention, but many readers will be too late to this aspect of fish husbandry, which is the point of this particular article.

A good professionally written article for prevention of aquarium disease is this one:
"Aquarium Disease Prevention; Proven Steps for a Healthy Aquarium"

Every single step in the above article should be followed to a T and I can guarantee that the incidence of disease will go down greatly.

Hopefully readers will acquaint themselves with this above referenced article which will in part form a basis for this article as I go forward.
As well this article is another good read before one goes forward with any fish treatment:
"Aquarium Medications; Part 1"

Gill, How to treat sick fish, 2 I cannot emphasize more that many if not most fish diseases, especially bacterial or fungal in nature (including secondary infections to parasitic infestations) have a background issue. Failure to eliminate this background issue(s) will often result in failure of treatment.
Often the "background issue" is more than half the problem, so a good part of the treatment plan is REMOVING this background issue!!
A good analogy I like to use as to why it is so important to eliminate these issues is this:
"Not correcting causes or background issues is akin to standing in a burning building asking for a treatment for burns, while not leaving the burning building"

Gill, How to treat sick fish, 3 Unfortunately in my dealing with questions of what one should treat for a given set of symptoms, I have found that for the majority of these questions, the person asking the question either only addresses underlying issues in part or not at all.
Often this is not because the person does not want to, but they simply do not have the means or the availability for whatever reason to do so.
I would also point out, and while this may seem a bit harsh, it is still the reality, and that is this is still not a valid excuse to continue to ask for alternative treatments or complain to persons such as myself that the treatment failed when proper procedures have not been completely followed.

I personally spend a copious amount of time writing articles, answering questions, or even paying staff to help for free, but please remember that one needs to obviously follow the medication course prescribed, but just as importantly if not more so, deal with ALL underlying causes to a given fish illness problem. So repeatedly going in circles when not following exactly advice given is in my opinion disrespectful to the person who is trying to help you with your fish illness issue.

When you are asking others for help, whether it be online or at your local fish store, make sure you ALWAYS provide background first; including ALL water parameters (mineral Cations too), filtration, maintenance, feeding, & fish kept. Past fish treatment history is important too.
I cannot tell readers how many times people have asked for my help and told me that their water parameters were OK/good, but when pressed to provide actual COMPLETE numbers or I went out personally and checked, the water parameters were anything but OK/good. Often the important KH & GH tests were missed too, partly due many well meaning aquarium keepers fooled into thinking that their "API Master Test Kit" was all they need (a symptom of shopping discounters or getting information from "cut & paste" internet articles, videos or forums).

As an analogy; your personal Doctor always has your history, takes your vital statistics, etc., so why should we expect those we are asking to help us with our sick fish to guess, especially when one considers we often are asking others to help us sight unseen and with far less tools at our disposal than a Doctor would have?

Here first are basic procedures to check off before treating any fish sickness issue:

Recommended Aquarium Parameters for healthy fish, disease treatment


Best Aquarium & Pond Medications
AAP Professional Aquarium & Pond Medications


Next, here are causes for failure of any fish illness treatment regimen:

Gill, How to treat sick fish, 4

Other Recommended Reference & Product Sites

Hydro Sponge Filter

AAP Hydro Sponge Filters

THE PREMIUM Aquarium Sponge Filter with as much as 5 TIMES the bio and mechanical capacity of commonly sold Chinese knock offs!!
Definitely worth the extra $1-3

UV Replacement Bulbs, LampsUV Replacement Lamps/Bulbs; Aquarium or Pond
For TRUE High Output, Hot Cathode, Low Pressure UVC Germicidal Bulbs, for aquarium or pond

PUR or RQE, YouTube Video Fail- Guide to lighting a planted tank

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!

TMC V2 RO Filter systems; the very best you can buy with TDS meter (far superior to 4 stage RO/DI systems sold via Bulk Reef Supply, Amazon, or eBay that use the inferior cellulose triacetate membrane made by Dow):
Reverse Osmosis Aquarium Water Filter, TDSReverse Osmosis Aquarium Water Filters; with TDS Meter

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TB in Fish, Mycobacterium Tuberculosis; Bettas & more


By Carl Strohmeyer-PAMR 40+ years experience
Updated 9-25-19

Betta with Fish Mycobacterium TuberculosisFish Tuberculosis is generally caused by Mycobacterium marinum, a bacterium closely related to the human TB (Tuberculosis) bacteria, Mycobacterium tuberculosis, although incidents of Mycobacterium triplex have also been reported with Bettas.

Despite some internet claims, based on my many years of "house calls" and other professional aquarium maintenance work has shown Fish "TB" to be relatively uncommon with the exception of cases where the bacteria has been passed around and the fish' immune system has been compromised, this is especially the case with recently confirmed Mycobacterium triplex.
This seems to be more common among breeding and showing circles/clubs where water equipment cross contamination is common.
The above said, be careful about assuming your fish have Fish TB, unless all symptoms are present and treatment for more likely infections have failed.

However Bettas and Gouramis for reasons not 100% known seem to be more susceptible or have been placed in conditions where tuberculosis is more likely to overcome the fish' immune response.
Please read the "PREVENTION" section for more about TB in Bettas in particular

Treatment for Mycobacterium tuberculosis is often long and not always successful, as well low fish immunity due to poor aquarium parameters (including Redox Balance), along with fish age or even simple stress from tank mates can add to treatment difficulties or make treatment impossible (especially since Fish TB is difficult to treat anyway)


A myth I have seen written in a few "circles" (for some reason I have found this myth especially common on certain Betta Forums), is that Fish TB can also cause full blown human TB which is simply not true (only mild localized infections in healthy adults humans).
However it is still best to avoid fish to human transmission, especially if your immune system is compromised in any way.
Generally when the Mycobacterium marinum bacteria infects humans it is a dermatological issue as the bacterium usually enter the skin via small abrasions or cuts when you are performing aquarium maintenance.
The symptoms in humans are usually restricted to skin and soft tissue destruction in most instances of Mycobacterium marinum infection via small purple lesions that can gradually grow. It is noteworthy that in my decades of professional aquarium maintenance with literally 1000s of aquariums, I have only noted a couple of proven fish to human TB transmissions, so be careful of alarmist web sites.

Another myth about Fish TB, especially since it seems to have become the aquarium fish disease "De Jour" (disease of the day), is its transmission.
Based on emails, phone calls and discussions with my maintenance friends, you would think every fish that is sick now suddenly has this disease.
While it certainly seems to be more common and virulent as per confirmed cases, it is NOT commonly present in an aquarium (unlike Aeromonas, Columnaris, or Pseudomonas bacterium).

So in the case of fish that have been living in an aquarium for months and often years without any outside exposure to other fish, the facts are it is impossible for the fish to suddenly come down with a Mycobacterium infection!
Usually this false diagnosis with no history of possible exposure is simply the result of a simply weak or old fish showing symptoms that are often common to Fish Mycobacterium (TB).
What is also very noteworthy with a fish that may be showing symptoms common to Mycobacterium, if the fish dies within days of the first symptoms, it is VERY LIKELY that your fish did NOT have Mycobacterium as generally Mycobacterium kills slowly!!

Even with potential exposure, in my experience with confirmed cases of Mycobacterium, transmission usually ONLY happens in aquariums with old, genetically weak, injured, or with poor tank water parameters (which includes a poor aquarium Redox Balance).
In other words, under normal conditions this is not a highly contagious fish disease!

Then as per poor water conditions, genetically weak, poorly fed, etc. fish, it is more likely the fish have another bacterial infection and correcting these conditions is job one. Most common with Bettas in particular is lack of mineral Cations resulting in poor osmoregulation and increased oxidative stress (poor Redox balance)


If staining for identification, Mycobacteria stain bright pink against a blue background (as these bacterium are acid fast).

However, most aquarium fish keepers do not have the ability to grow cultures or make slides; so the symptoms of Fish TB are usually wasting away, lesions on the fish' body, loss of scales and/or coloration, and especially skeletal deformities such as curved spines.

largemouth bass showing clinical signs consistent with mycobacteriosisThe Betta fish in the picture above (please click to enlarge) displays classic symptoms of Fish TB in finage, skeletal deformity, and wasting to the point light can slightly penetrate her abdomen as seen in the light spot.
From Testing for "Fish TB"; AquariaCentral

The fish to the right is a largemouth bass showing clinical signs consistent with mycobacteriosis; note the ragged fins, sores, and general deterioration of the fish, differing from more common fish diseases such as Aeromonas and Columanaris.

Mycobacterium triplex can only be identified by 16S rDNA sequencing, so positive identification is difficult.


As with ANY fish disease, always start with getting your aquarium water parameters in order (as well as feeding), which in most my client house/office calls over the years with TB or copycat fish diseases this was a major issue.
Reference this article for more in depth help here:
A Healthy Aquarium, Fish Disease Prevention

Mycobacterium marinum
Time of Treatment is VERY long and is generally administered for at least three months. Cure rate is well under 50%, but also do not believe those who state it cannot be cured as I have many times.
A hospital tank treatment is advised for fish TB since this generally is a very long treatment regimen and a three month treatment of ANY antibiotic can result in serious damage to your aquarium bio filter.

The three most proven antibiotic methods, which can and should be used in a combination of two of these drugs along with the other described alternative treatments:
*Kanamycin (Kanaplex)
*Isoniazid (from Aquarium Medications Part 2)

Sometimes a Sulfamethazine/Trimethoprim Combination can be effective too.
*Sulfamethazine/Trimethoprim Combination (sometimes effective)

Often a "cocktail" of these medications along with a fish bath (mentioned next) is needed for any hope of success, which can be very harsh on the aquarium environment. So unless the infection is systemic, a hospital tank might be best (adding a TRUE level one capable UV Sterilizer to your main tank is suggested to check spread, see later in the prevention section of this article.

A fifth consideration, albeit less field tested (it does show lab results though) is Usnea, which from my experience should only be administered in a "Fish Bath" form for 30 minutes. Methylene Blue should also be used in this bath, but no other antibiotics should be used in this bath with Usena.
These baths can be rotated; meaning one bath with Usena and Methylene Blue and the next bath with MB along with one or two of the other antibiotics, then back to the Usnea

Usnea is best as a used as a bath ALONG with an in tank treatment with one of the first three noted medications (or better hospital tank).
Further Information: Organic Fish Treatments; Usnea

A sixth consideration is Allicin, the active ingredient in RAW Garlic. Mycobacterium marinum) has been demonstrated to be effectively treated with Allicin, at least in vitro.
SeaChem Garlic Guard can be used in a fish food slurry preparation and mixed with both Neomycin and Kanamycin for improving the potential effectiveness of tuberculosis treatment.
See: Fish Nutrition; Garlic

Recommended Product Resource:
Garlic Guard; for Fish TB, Appetite Enhancer

A final consideration that might be helpful, in particular if the diagnosis is INCORRECT (which is common), is the use of Medicated Wonder Shells. These address many aspects of fish health, including problems that are simply symptoms of fish old age and not any disease in particular.
While a Medicated Wonder Shell is not a strong treatment for any particular disease, these are helpful as both follow up treatments and mild treatments that also address essential water parameters that might be out of balance (such as Redox).

Recommended Product Resource:
Medicated Wonder Shells

Back to Fish Baths; regardless of the medication or combination of medications used in tank, I suggest a Fish Bath with one of the first four before mentioned treatments (not garlic) at least once per day during this time period.
In fact in some cases the fish baths were all that was needed for success assuming these were carried out regularly.

Now for the bad news, from experience and others, once the fish became emaciated I had little to no success saving them.

Please Read/Reverence these Articles:
*Aquarium Medications; How Medications Work, and Which Ones to Use and Not to Use
*Fish Baths, How to Perform

Treatment of Mycobacterium triplex (not M. marinum) in human studies has shown it to be nearly impossible with only reduction of symptoms, not eradication of the bacterium.
These treatments used levofloxacin, ethambutol, and clarithromycin; all of which NOT available in fish medications.
You best bet with this rare strain (assuming your fish even has it), is to sadly euthanize and sterilize EVERYTHING, then start over.

How NOT to Treat:

The use of salt either in baths or in the aquarium will have absolutely no affect on Mycobacterium tuberculosis since this bacterium thrives equally well in salt or freshwater.
Temperature increases or decreases have little effect and in fact a temperature increase over 30°C. (as with Columnaris) often worsens a Mycobacterium tuberculosis infection.
Temperature decreases has shown some anecdotal slowing of the progression of Mycobacterium tuberculosis, but no cure.


There is not a 100% proven way to prevent Aquarium Fish Tuberculosis (as with most pathogens), however based on my own observations going back to 1977 (working at a Pet Store Fish department and then my aquarium maintenance company), I definitely noticed patterns.
Emails from customers and questions I see asked in forums and elsewhere have added to this same pattern.

Here are a few known factors:

Further References:
*Aquarium Cleaning
*Aquarium Chemistry; In Depth, from Beginner to Advanced
*Aquarium Redox for Fish Immunity, Health

The use of Aquarium UV Sterilization with a correctly applied UV Sterilizer performing at Level 1 Sterilization (this will NOT and CANNOT be achieved with the many low end UV Clarifiers such as the Green Killing Machine, AquaTop Hang On and similar water clarification ONLY devices flooding the market!).
The correct use of a UV Sterilizer can aid in Redox Balance and in the end also aid in fish immunity and is a MUST for an aquarium with a history of Fish TB to check the spread based on my extensive experience with Fish TB and true UV Sterilizer use.

MUST READ Reference:
Ultraviolet Sterilization, Facts & Information; Including Level 1 & 2

Recommended Product Sources:
Level 1 & 2 UV Sterilizers
Clay Neighbor's AAP Custom Super Premium Fish Food; Far Ahead of any other!

The use of SeaChem Garlic Guard or similar in fish food can also be used in an ongoing basis to improve fish health and prevent Fish Tuberculosis.

Back to Bettas in particular, a problem I have seen based on patterns that are almost 100% identical and that is many Betta Forums and Clubs will pass around the same methods of Betta keeping that can increase the likelihood of TB infections.

This includes constant chasing of pH, 100% water changes, keeping of Bettas in very small closed environments, lack of positive mineral ions essential to immune response, passing around fish (with constant exposure and stress), and limited gene pools due to interbreeding.

My suggestion is to keep your Betta in a system with a larger volume of water with small individual containers.

Within this system these practices can aid in TB prevention:

See also the articles below in the references/resources dealing with Aquarium Disease Prevention for more help in Fish TB prevention

Further References/Resources:

*Mycobacterial Infections of Fish
*Fish Diseases; Univ. of Florida
*Aquarium Disease Prevention; Proven Steps
*Mycobacterium triplex Pulmonary Disease in Immunocompetent Host

By Carl Strohmeyer
Copyright 2019

Other Suggested Resources, Products

*Aquarium information for prevention of fish tuberculosis, TB
Well researched and up to date aquarium and pond answers, help, and links

*Columnaris in Aquarium Fish (also Fungus)
This is easily the most in depth and regularly updated on the subject of Columnaris and Fish Fungus to be found ANYWHERE on the Internet!

*The Aquarium Nitrogen Cycle
The most up to date article on the subject of the Aquarium Nitrogen Cycle, based on both research and 35+ years of professional experience with 1000s of client aquariums!

*Aquarium UV Sterilization for prevention of fish tuberculosis, TB
UV Sterilization

This article covers many aspects of Aquarium & Pond UV Sterilization from how, why, facts, myths, and maintenance including the importance of changing UV Bulbs regularly.

*Aquarium, Pond UV Lamps, Bulbs

UV Bulbs; Page 1

As noted above, changing these PREMIUM bulbs/lamps every 6-12 months is essential for a properly functioning UV Sterilizer

*Aquarium Silicone Sealant; USDA 100% Fish Safe
100% Fish Safe, USDA & Agricultre Canada approved, the same CANNOT be said for Hardware Store brands!
Excellent for building aquarium systems of multi-tier fish housing.

Aquarium Lighting; Basic, Reef, Planted

The above referenced article is easily the most in depth and regularly updated on the subject of Aquarium Lighting to be found ANYWHERE on the Internet!

Atison's Spa Clear; Indian Almond Leaf Conditioner

Clear Betta Spa contains wild almond leaf extract to simulate the natural environment of the native soft water fish.
Other natural botanicals, including Yucca extract, help control ammonia, reduce stress and maintain cleaner water.

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

*Planaria & Detritus Worms in Aquarium; Which is Correct?


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Fish Baths, Dips, Swabs; Including Coral; For Disease, Ammonia, Treatment


Fish Baths/Dips for supplemental (& even primary) treatment of Bacterial infections, wounds, sores, Fungus (Saprolegnia), parasite infestations & more

By Carl Strohmeyer-PAMR 40+ years experience


Aquarium Fish BathsUpdated 6/27/23

Although the Article; "Aquarium Disease Prevention" has a relatively in depth explanation of how to perform (& why) a fish bath or dip, this Aquarium Answers post/article will hopefully expand more on this subject for a better understanding. I am also including input from members of Everything Aquatic Forum to further assist in this article.

*Principles of Aquarium disease Prevention and Treatment
*Everything Aquatic; Aquarium Forum Board
*Everything Aquatic; Performing a Medicated Fish Bath

The use of Swabs and Dips is also discussed in this article.

Why a Fish Bath (both positives and negatives)?

The basic ingredients of a bath include:

What is a Bath or Dip used for in the Treatment of Fish Diseases or Similar?


What is Better; a Bath or Dip?

This is a subjective question that can not be simply answered however I will give some generalizations.
A properly performed bath is much less stressful to the fish than most disease that they are being treated for. The most stressful part is capture of the fish which can be minimized with a breeder/holding net or proper netting.
In fact I have seen fish bounce back from baths within a hour, especially when the use of stress reducing and medicated water conditioner is used directly on the fish and in the water as the fish is returned to the aquarium. The best product for this by far is the professional water conditioner AAP Res-Q.

Resource: AAP Res-Q

So with this in mind a mild to moderate infection or for many quarantine purposes the bath is the better choice.
As well almost any injury is better treated with a bath since stress is a major factor with an injury.
I often use baths over in tank treatments where “tank wide infections” are not present so as to not interfere with the biology of the aquatic environment in any way.

A dip is often a choice of last resort for seriously ill fish, especially with Dropsy, bladder infections or other infections causing osmoregulation problems.
One exception for healthy fish where I often choose a dip over a bath is for the prevention of Ich, Cryptocaryon, Oodinium and similar parasite infections.
I have not seen a healthy fish ever succumb from a dip when used for this purpose and a dip is nearly 100% effective for such prevention in marine fish, however less effective and more harsh for freshwater fish (provided there is not latent infection already in the aquarium).

A dip is NOT a good choice for seriously injured fish or fish that have considerable open tissue due to infection, as the dip will often make this worse by extracting necessary body fluids that are already being lost. For these fish, the bath is the vastly better choice.

Performing a Fish Bath

(expanded from Aquarium Disease Prevention);

A bath can be performed in as little as 1 quart of water, in a 1 gallon Rubbermaid (or similar) container or a small BARE tank. Generally the larger the better since it is easier to maintain dissolved oxygen levels and figure out the amounts of medication (if used) in larger containers
If I use a 1 quart container, I would use 1/4 teaspoon of salt and several drops of MB (I also recommend rubber gloves and old towels, rags, paper, etc spread around since Methylene Blue is messy and stains).

The schedule is generally 20-30 minutes at least once per day, twice if the fish will tolerate this frequency.

For freshwater I would add Methylene Blue at double normal tank treatment strength (as per bottle instructions) then add salt (NaCl) at about 1 teaspoon per gallon. With the Premium AAP 5% solution "MethyBlu" (recommended), this means 2 drops per gallon
Epsom Salts can also be used too at 1/4 teaspoon per gallon in baths used for treatment (some use higher amounts, but I find this works well when combined with sodium chlorides salt). Epsom Salt is especially useful in cases of bloat, water retention, swim bladder issues, etc. This salt should be pre-dissolved prior to introduction of fish to prevent burning of gills.

The salt (regular salt; NaCl) can be increased for difficult treatments (such as Columnaris), especially with salt tolerant fish such as livebearers. Sodium Chloride (NaCl salt) is not only helpful for many external bacterial issues, it also acts to pull fluids through the fish' body often helping with internal osmorgulation issues.
It is best to slowly add dissolved salt to increase levels gently in salt amounts over 3 teaspoons per gallon, even in salt tolerant fish.
Generally for most fish (even catfish based on University of Florida studies) 2 teaspoons per gallon can be tolerated for up to 30 minutes (many fish can tolerate 4 teaspoons per gallon), although if unsure about your fish’ tolerance, gradually add the salt via a dissolved solution during the first half of the bath.

Epsom salts (Magnesium Sulfate) are useful for baths (I do not recommend even short term use in the main display aquarium) in either fresh or saltwater where internal issues are suspected, including constipation and lack of appetite.
This said, Epsom salts are generally not enough alone except for very specific internal bloating issues and other more specific medications will need to be added to the bath (read further in this article, including references/resources).

Lees Net Fish Isolation Box for sick, injured fishIMPORTANT TIPS; Please Read Before Performing a Fish Bath:

Please see the video at the end of this article for more help in understanding the process of a fish bath

Further Bath Tips from Everything Aquatic Member Fishfever

  1. Always spread out an absorbent mat around the tank before doing anything to catch drips (and especially Methylene Blue, ***IT REALLY STAINS IF IT GETS ON ANYTHING ***). Gloves are good too to avoid the blue finger syndrome!

  2. Premixing the salt with tank water in a large container saves time if you plan to give a number of baths. You could probably premix the MB also (not sure) but would not mix Potassium Permanganate since it reacts with tank water (I think it removes dissolved organic compounds in the tank water).
    I use an eyedropper to get the proper fraction of a teaspoon to gallon ratio for the Potassium Permanganate in the small bath container or double bag (it's not a perfect ratio but it's consistent).
    Product Source: Potassium Permanganate from AAP

    Further Information: Aquarium Medications 3; Potassium Permanganate

  3. If possible, give your bath in a container or double bags within the tank.
    This way the bath stays heated to the same temperature as the tank and if the fish jump they just jump into the tank. I fill my bath container or double bags just enough so they still float and the buoyancy pushes the container up against the rim and top cover, keeping it from trying to flip over.
    If you overfill the bath container will sink. Remember to float the bath container or bags in your tank long enough to equalize temperatures.

  4. Since I have to give twice daily baths, I leave the fish in a small breeder net (about 6"x6"x4") overnight after the evening bath which I do just before I shut the tank light out and go to bed. This saves me from having to catch the fish for the morning bath, i.e. only have to catch her once a day for the evening bath.

Bath/Dip Risks

Obviously there are risks in the performance of a fish bath or dip, however in fish less than 6 inches these can often be minimized as per previously suggested tips.
For minor injuries or infections sometimes the risk of stress is simply not worth the bath, HOWEVER in my experience with literally 100s (if not 1000s) of baths/dips the risks for most applications is far less than the alternative.
Even with 'extreme' freshwater dips used for saltwater fish, whereby the fish will react as if they are dead, the fish will generally “snap out of it” in a matter of hours and will be better than before this dip.
Most baths are much less stressful than the previous example, so any observed stress will pass quickly if the bath is performed correctly.

As well in many cases such as sores or diseases, the use of a bath will allow for a more mild in tank treatment which is quite bluntly better for long term aquarium health than dumping in “tons” of harsh medications (especially when a hospital/treatment tank is not available).
The bottom line is to not let the bath/dip stress you more than the fish, as this procedure can often mean the difference of a successful treatment and an unsuccessful treatment especially in severe cases of Ich (this is especially true with sensitive fish such as Loaches) or in often difficult to treat bacterial infections such as Columnaris.

Further References:
*Aquarium Ich in Freshwater or Saltwater
*Columnaris & Fungus in Aquariums

Medications in Baths;

Another option to baths is IN ADDITION to the salts and Methylene Blue, but NOT combined with Potassium Permanganate, is you can safely add many antibiotics at double normal "in tank" recommended dose for the 30 minute bath. This can both increase the effectiveness of the bath and the antibiotic added.

Before I go on here, it is noteworthy that with any aquarium/pond fish treatment it is important to know all the steps as often treatment is much more than a medicated fish bath or dumping medication into an aquarium.
Please read this article before ANY aquarium treatment regimen:
Fish Diseases | How to Treat Sick Fish

Medications that generally are good choices for baths are;

Alternatives to Methylene Blue

Acriflavin, at double recommended tank dose can be substituted for Methylene Blue for treatment baths for ailments such as wounds, and very stubborn fungus infections (which can be common in bettas kept in confined spaces).
Product Source: API Yellow Powder, Nitrofurazone & Acriflavin

Kordon Fish Therapy Curative Bath, This is an all natural fish bath developed by Kordon containing natural therapeutic oils (including citrus, neem, and lavender oils), and aloe vera.
However do not be fooled thinking that just because it is natural, it is therefore better, as this is NOT a replacement of Methylene Blue for fish suffering from ammonia poisoning, low oxygen damage, pH shock, or other bath medications for more serious problems.

This product is best used without any other medications as an alternative treatment or preventative for suspected mild to some moderate problems, in particular if parasites are suspected (either internal or external). Use with salts is OK and suggested for moderate to serious issues (either or both Epsom Salt or Sodium Chloride).

Potassium Permanganate (at double recommended tank dose) can be substituted for Methylene Blue for treatment baths for ailments such as Flukes, cloudy eyes, & some stubborn parasite and bacterial infections such as Columnaris(generally Potassium Permanganate is the better choice for Columnaris unless the fish is displaying rapid breathing or is on "death's door").
Product Source: AAP/Jungle Potassium Permanganate, Clear Water

HOWEVER for "pure" preventative baths, ammonia poisoning or unknown problems, Methylene Blue is by far the better choice.

Unlike Methylene Blue; DO NOT mix Potassium Permanganate with antibiotics.

See this article under Potassium Permanganate or Methylene Blue for more:
Aquarium Medications; Chemical Treatments.

Another key point is that Methylene Blue can quite SAFELY be overdosed as it takes high amounts with long term exposure to be toxic, while Potassium Permanganate should NEVER be overdosed.

CAUTIONS About the Use of Potassium Permanganate for Baths & Painting (Swabbing) Infections:

Since Potassium Permanganate is strong oxidizer, caution should be exercised in usage for baths and especially as direct application for external infections (unlike Methylene Blue which is very difficult to over dose).
For most fish, a double dose of the normal 'in tank' recommended dosage is used.
This varies from product to product, however using Jungle Clear Water as an example; the recommended tank dosage is 5 mL per ten gallons, so the bath dosage would be 10 mL per ten gallons (or 5 mL per 5 gallons of “bath” water).
Fish such as many Tetras, Loaches, and similar “sensitive” fish should be given consideration in dosage of Potassium Permanganate.

An even more important consideration is the use of Potassium Permanganate for direct application/swabbing of certain infections such as external symptoms of Columnaris or Saprolegnia/Fungus (see the next section for more about swabbing/dips).

Potassium Permanganate should be diluted at least 3/1 up to 2/1 (water/PP) for this use and often more so depending upon the fish in question (testing on a healthy part of the fish in question or a related fish may help determine tolerance).
As well do NOT use even diluted PP anywhere near the gills of a fish, or on fish tissue showing signs of necrosis [1], THIS CAN BE LETHAL.
Use a diluted PP swab ONLY on areas of actual Columnaris, Saprolegnia, or related infection such as the common "Saddleback" often seen in Columnaris or the fuzzy growth areas of Saprolegnia.

If Potassium Permanganate or Hydrogen Peroxide is accidentally applied directly to the gills, an immediate 3-5 minute dip in water with a 2-3 x normal dose of SeaChem Prime or other similar water conditioner is a must!
The use of AAP Res-Q or Prime or other similar water conditioner at double strength in a 2-5 minute dip (using tank water) is also strongly suggest after a bath using Potassium Permanganate or Hydrogen Peroxide if only to help restore the slime coat and restore the fish Redox Balance since most aquarium water conditioners are temporary Redox Reducers.

Product Sources:
SeaChem Prime, Temporary Redox Reducer AAP Res-Q; Premium Medicated Bandage, Reducer, & Slime Coat Protector

Further Information: Aquarium Water Conditioner Review

Please note that this point of dilution does NOT apply to Methylene Blue which is safe to use full strength, even around gills (although internal gill application is best performed via a bath, not a swab).

Dips, Swabbing (Swabs), etc.

In a dip, I again adjust pH and add Methylene Blue, HOWEVER in the case of the marine fish, I will use a specific gravity of 1.001 (basically a freshwater dip) and a specific gravity of 1.012 of 1.015 for the freshwater fish (2.3 oz. or approximately ¼ cup of fine salt per gallon) which is basically a saltwater dip.
This dip should be no less than 3 minutes and no more than 5 minutes to be effective.

Ocellaris Clownfish in freshwater dip for Oodinium treatment or prevention For known problems (or sometimes as a preventative for new fish especially as a Cryptocaryon or Oodinium in marine fish) a 3-5 minute dip is sometimes even more effective, albeit more stressful to the fish (more stressful for freshwater fish than saltwater fish).
The picture to the right displays an Ocellaris Clownfish in freshwater dip for Oodinium treatment.

To lower the stress a high salt dip for freshwater fish or a freshwater dip for marine fish it is advisable to use the first 2 minutes (of a 5 minute dip) slowly introducing the saltwater (or freshwater for marine fish) until the fish is in the desired salinity water for the remaining 3 minutes.
Make sure that the water added slowly during the first 2 minutes is pre-mixed with salt prior to use for freshwater fish or pre-adjusted for pH for marine fish.

A dip is often a better choice than a bath for a large or otherwise “spastic” fish due to the much shorter duration.
As well a dip, albeit much more harsh than a bath (when used as described), may be a better choice for a very ill fish that may be “at deaths door” and the risks of a dip are low when compared to the fact of the probable imminent death of the fish anyway.
A dip is also a good choice for problems that stem from fluid build-up and poor osmotic function, such as many causes of “Pop-Eye”.

*I also use dips to replace quarantine when quarantine is not possible for fish of questionable sources; especially with marine fish as a dip is nearly 100% effective for destroying Oodinium or Cryptocaryon on marine fish (the osmotic pressure causes the parasite cells to burst). Keep in mind that the dip does not destroy these parasites in the water column if the disease has already been accidentally introduced.

Further Reading:
*Oodinium in Marine Fish
*Marine Ich, Cryptocaryon


AAP Wound Control, MerbrominAnother similar idea is to directly drop or “paint” with a Q-Tip (or similar implement) Methylene Blue, Mebromin (AAP Wound Control), Potassium Permanganate (diluted), tincture of Iodine, or Hydrogen Peroxide onto a problem area such as Saprolegnia/fungus, Columnaris, Ichthyophonus, or similar.
This can be VERY effective for stubborn external infected areas on a fish (such as node on fish tails, etc.) as well as a first response to a wound or injury.

The negative of swabs is these can be even much more difficult to perform for a nervous fish keeper than a bath, so staying calm is very important. As well, while remaining calm, it is best to firmly but gently handle the fish so as to prevent injury. I prefer using my hands once captured, not a net.
For larger specimens I will use a smooth container with square sides to more easily hold the fish firmly.

Methylene Blue is safe to use for exposed tissue, which will stain blue, but this is not a danger unless grossly over used. However since MB is not very strong, if the area treated still has a slime coat, MB will likely not penetrate well (a swab may not also be called for in such an instance).

The use of Methylene Blue at full strength (in a typical 2.303% solution or concentrated MethyBlu) as a swab, dip, and to a lesser degree a bath will also expose healthy or at least normal tissue as Methylene Blue will generally adhere to infected areas or wounds staining the area “blue” due to the lack of the normal “slime” coating fish have on healthy areas of a fish’ epidermis.
Even scar tissue will generally not stain “blue”, so this a good test of whether or not a “growth/sore” is actually an infection or similar (please note that some cancers/tumors can mimic healthy tissue and not stain blue).

Another alternative to a straight Methylene Blue swab or drops is Mebromin
In fact prior to the demise of availability of this Mebromin around 2002, this was my swab or drop chemical of choice for many applications over Methylene Blue.
While Mebromin does not have the benefits of dying exposed tissue (showing where tissue is compromised) and transport of oxygen to cells, it actually is far more effective for exposed injuries/wounds and severe infections caused by opportunistic bacteria with just as much safety margins as Methylene Blue (unlike Potassium Permanganate and Hydrogen Peroxide) but is vastly more effective for bacteria such as Columnaris and in fact is the swab/direct application of choice in such bacterium.

For really serious exposed infections, such as flesh eating bacteria (which is difficult to treat), is a combination where the aquarium fish keeper first uses AAP Wound Control to stop & kill the infection, followed by placing the sick fish in a holding container for 5-10 minutes then follow with a MethyBlu swab which although not as effective on bacterium, it is better at promoting healing and getting oxygen to sick tissue.

Product Resource: AAP Mebromin (Wound Control)

For serious infections such as advanced cases of Columnaris/Sadddleback Disease, a swab with Merbromin (AAP Wound Control) or Potassium Permanganate (as discussed earlier in the article in detail) should be performed, then possibly follow a couple hours later with AAP/SeaChem StressGuard.
As already noted, some sores, blisters, tumors, etc., may not allow adhesion of Methylene Blue/MethyBlu and AAP Res-Q may not be enough, this is where the use of Merbromin or maybe Potassium Permanganate may be called for.
Please Review "Potassium Permanganate Cautions" before using.

If Potassium Permanganate or Hydrogen Peroxide is used as a swab; placing the fish into a quick dip utilizing a double dose of any Redox Reducing Water Conditioner such as SeaChem Prime,AAP Res-Q, or AAP Sheildex can immediately stop any unwanted oxidation of Potassium Permanganate on the fish.

Product Sources:
Prime Aquarium Water Conditioner from AAP
Potassium Permanganate; Clear Water from AAP

Further Information about Redox: Aquarium Redox

After swabbing, the use of AAP/SeaChem StressGuard in the aquarium is suggested.

Product Resource:
StressGuard from AAP

For stubborn Fin rot or infections direct application of 3% Hydrogen Peroxide via swab has been successful on many occasions.
Further Information: Aquarium Medications 3; Hydrogen Peroxide

Potassium Permanganate (this should be diluted approximately 50% to 60%, unlike Methylene Blue) & Hydrogen Peroxide are generally more effective for the above noted infections.
However open sores, wounds, and in particular gill problems should Not use Potassium Permanganate.

Hydrogen Peroxide or tincture of Iodine may be used (EXCEPT for gills), however Methylene Blue is a better choice direct gill applications where PP or Hydrogen Peroxide will burn the gills and often kill the fish as a consequence.

If Tincture of Iodine is used as a swab, a quick dip into some "throw away" water after the swab can help prevent toxic levels of iodine in the aquarium due to excess iodine on the fish after the swab.

Any of these swabs can also be used in conjunction with baths and "in tank" treatments too.

Finally, for stubborn fungal infections, Acriflavin (found in API Fungus Cure) is another good swab choice, especially for Bettas normally kept in small tanks/bowls.


Often a dip of anemones or coral (such as Acropora corals) is necessary to remove bacterial, parasites, planarian, etc.
Further Reference: Fish Parasites, Flatworms, more

A simple freshwater dip using de-clorinated freshwater adjusted to the pH of the water of the saltwater containing the specimen to be dipped is often "good enough" for many problems.
This should be between 3-5 minutes to be effective for "bugs" such as Oodinium.

Iodine Baths are excellent for some potential parasites of corals such as flatworms.
For a home method, the use of Tincture of Iodine 2.5% can work well and is available over the counter at most drug stores.
Use 1 Liter (approximately 1 quart) of Tank water, then added 20 drops of Tincture of Iodine 2.5%. Then fill a second container with tank water only, this is for rinsing dipped (bathed) corals.

Place your corals including both SPS and LPS in this bath for approximately 20 minutes (do NOT exceed 25 minutes).
This is followed by rinsing the corals gently in the rinsing the corals for about 30 seconds with a swirling motion.

An excellent and SAFE product to use is SeaChem Reef Dip, which contains elemental iodine complexed to a protective slime coat for safely and gently disinfecting corals.
SeaChem Reef Dip can be used prophylactically or to remedy diseased specimens. It is safe to use with both stony and soft corals. It is also safe for anemones and polyps.
Product Source: Reef Dip; Contains Elemental Iodine Complexed to a Protective Slime Coat


(Use accurate teaspoons, not silverware):

Fish Bath Video;



Just like to thank you for the information. Our fish is doing GREAT! I wish I had a before and after picture. He had turned completely black lost so much weight and his tail was almost completely gone. I really didn’t think there was much of a chance that he’d make it. I did the fish baths with Aquarium salt, Methyl Blue, Kanaplex, and Metronidazole for 10 days. Now he has gained weight and has almost caught back up w/ our other fish. He has turned back completely to gold except his fins which were black to start with. Its truly amazing. My girls would have been heartbroken if he had not made it.

Thanks again.
Jennifer Arnder

Glossary of Terms

*[1] Necrosis: Localized tissue death that occurs in groups of cells in response to disease or injury. This often results in large growing sores and exposed deep tissues of the fish.

Related Tips:

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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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