Fish Baths/Dips for supplemental (& even primary) treatment of Bacterial infections, wounds, sores, Fungus (Saprolegnia), parasite infestations & more
Updated 11/06/09


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.

The basic ingredients of a bath include:

• Salt (Sodium Chloride)
• Methylene Blue (this can be substituted with Potassium Permanganate in certain instances)
• Occasionally Epson Salts (Magnesium sulfate) can be used as well
• Further medications can be added (this will be addressed later in this article)

What is a bath or dip used for in the treatment of fish diseases or similar?

• Treatment of sores or injuries, especially open sores that expose deeper tissues (often minor injuries do not require a bath/dip). The Methylene Blue will stain tissues and aid in prevention of bacterial growth, as well Methylene Blue will increase available oxygen to tissues. Swabbing (or dripping) the wound, sore, or red streaks (caused by Septicemia) with Methylene Blue prior to a bath often increases the effectiveness.
• As an Aid to Ich, Velvet and similar parasite infections. Although a bath or dip is not an effective cure for in tank Ich infestations or similar, a bath/dip can increase survivability in severe cases as the bath/dip provides critically needed oxygen to gills/tissues (via the Methylene Blue), as well Methylene Blue will often stain the parasite on the fish and weaken it severely (keep in mind that Methylene Blue was used as an early Malaria treatment, and that Malaria is a protozoan as is Ich and Velvet). The use of baths/dips with sensitive fish such as Clown Loaches is often a must in my experience for moderate to severe Ich (Ichthyophthirius) infestations.
• As an aid to bacterial infections (such as Columnaris) or Saprolegnia (Fungus). As with wounds/sore, swabbing or dripping the Methylene Blue directly on areas of infection greatly increases effectiveness.
• As an aid to and for treatment of osmoregulation problems in fish such as Bloating and even Dropsy.
• As an aid to ammonia/nitrite poisoning, often as the result of poor handling/shipping and over crowded condition prior to an aquarist obtain a new fish. The Methylene Blue with be absorbed into the blood, kidneys, and liver where is can help lessens the effect of ammonia and nitrite poisoning.

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 (the most stressful part is capture of the fish which can minimized with a breeder/holding net or proper netting). In fact I have seen fish bounce back from baths within a hour.
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, somewhat less for freshwater (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 (or even less) or in a 1 gallon Rubbermaid (or similar) container or a small BARE tank (not gravel, décor though). I generally use a 1 quart pitcher with ½ 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).

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 (Epsom Salts can also be uses at 1/4 teaspoon per gallon in baths used for treatment, especially in cases of bloat, water retention, selling, etc.).
The salt (regular salt; NaCl) can be increased for difficult treatments, especially with salt tolerant fish such as livebearers (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.

A few more tips:
• I also recommend keeping the “bath” container in a location that does not allow the temperature to drop more than 2 degrees during this time so as to prevent shock when transferred back to the holding/display tank.
• If at all possible I recommend keeping the fish that are being given baths in a Breeder Net Box (see picture) or similar in the tank or in another filtered bare tank so as to make capture easy and less stressful for both you and the fish (if too much stress is incurred capturing the fish for each bath, this can negate the positive effects of the bath).
• ALL baths should start with water from the fish’ holding tanks water, so as to avoid pH and temperature shock. As well, ALL baths should have fresh Methylene Blue, salt & other medications if used, otherwise many medications can and will degrade and be less effective or even toxic in some cases.
The bottom line here is to throw away all bath water after completion of each and every bath.
• Floating pre-made fish bags of the dip water (with salt and Methylene Blue, do not add medications until immediate use) can make the bath process easier as everything is ready to go when you may be in a hurry. As well this allows for the correct water temperature.
• Although most bottles of Methylene Blue do not come with a dropper any more, I recommend finding a dropper that will fit the bottle or use an eye dropper so as to limit MB stains/mess.
• I generally do not recommend baths for larger fish (unless you are sure of your fish handling abilities), such as over 6-8 inches (15- 20 cm.), as often handling of these fish can be difficult and cause quite a mess. As well larger fish can be more easily injured due to the difficulty in handling them.
However, if a larger fish is in poor condition and question arises that the fish is already in a severely weakened condition, a bath or better, a dip may be attempted (see below for more about “dips”)

For saltwater I would add Methylene Blue at double normal tank treatment strength the Dilute the saltwater to 1.015 to 1.009, making sure your pH stays up by adding any buffers necessary before adding fish (1.009 is a must for Cryptocaryon prevention/removal).
The purpose of adding or lowering salt (whether SW or FW) is to change osmotic pressure which is an aid to parasite removal as most parasites such as Ich or Cryptocaryon cannot tolerate these changes as well as fish.

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).

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 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.

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

Medications that generally are good choices for baths are;

* Metronidazole which is s good choice for intestinal infections since it is not readily absorbed through the intestines.
* Kanaplex OR Minocyline for Columnaris, Dropsy.
* Nitrofurazone for Aeromonas or Furunculosis
* Usnea is an experimental alternative that has similar properties to Metronidazole and can also be effective for some viruses and possibly tumors. I use about 1 tablespoon per 6 oz. preparation for a 1 quart bath.
Please see this article for more about Aquarium Medications: “Aquarium Medications/Treatments; How they work”

Alternative to Methylene Blue

Potassium Permanganate can be substituted for Methylene Blue for treatment baths for ailments such as Flukes, cloudy eyes, & some 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").
HOWEVER for "pure" preventative baths, ammonia poisoning or unknown problems, Methylene Blue is by far the better choice.

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 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. 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 (see the next section for more about swabbing/dips). Potassium Permanganate should be diluted at least 3/1 (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.
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, etc.

For known problems (or sometimes as a preventative for new fish from questionable sources) a 3-5 minute dip is sometimes even more effective (albeit more stressful to the fish). 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 for the saltwater fish 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). This dip should be no less than 3 minutes and no more than 5 minutes to be effective.
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 premixed 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 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.

*Another similar idea is to directly drop or “paint” with a Q-Tip (or similar implement) Methylene Blue, Potassium Permanganate, or Hydrogen Peroxide onto a problem area such as Saprolegnia/fungus, Columnaris, or similar. This can be VERY effective for stubborn external infected areas on a fish.
Potassium Permanganate & Hydrogen Peroxide are generally more effective for the above noted infections (but also should be diluted, unlike Methylene Blue), however sores, wounds, and in particular gill problems should Not use either Potassium Permanganate or Hydrogen Peroxide, rather Methylene Blue is a vastly better choice (again especially for direct gill applications where PP will burn the gills and often kill the fish as a consequence).

The use of Methylene Blue 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).

A FEW HELPFUL CONVERSIONS
(Use accurate teaspoons, not silverware):
*Teaspoon = 4.929 mL
*Tablespoon = .5 fl. oz. = 14.787 mL
*For mixing salt for a dip; 1/2 dry cup will make a specific gravity of about 1.023- 1.025; For 1.015 specific gravity for a dip, use approximately 1/4 to 1/3 dry cup.

Fish Bath Video;