INTRO
It’s getting harder to find a good reference for performing a Formalin bath treatment for marine fishes. I’ve run out of them, to tell you the truth. Ones I used are no longer posted.
So, I thought I would share with the reader how I perform a Formalin bath treatment. It should work for the novice and experienced marine aquarium hobbyist. Just avoid ad libs and trying to take short cuts.
BACKGROUND and THEORY
Formalin is a combination of Formaldehyde gas dissolved in water. Formalin is typically about 37% to 40% Formaldehyde. For this purpose and post, I assume it is 37%. Formalin isn’t stable and has a short shelf life, the Formaldehyde breaking down to other chemical impurities that dilute the full Formaldehyde content. Unfortunately, the break down products are poisons to our marine fish. So obtaining and using only fresh Formalin is part of the requirement. What helps to remove some of these impurities is allowing the bath to sit, mixing with an airstone. Unfortunately, mixing is unreliable to guarantee removing the poisons (not to mention then the bath will be the wrong concentration of Formaldehyde), but nonetheless part of the procedure.
Use fresh Formalin. Do not use if there is any sign of precipitate or solids in the liquid.
Formaldehyde is a very active chemical. That is, it chemically reacts easily. It is a poison to our fishes in excessive quantities AND if the fish has an open wound, Formalin/Formaldehyde will kill the fish. Thus fishes with any kind, no matter how small, of an open wound must not be given any kind of Formaldehyde treatment, no matter how much it may be needed. This means fishes with injuries, fishes with lesions, and fishes showing signs of coating and skin loss must not be treated with Formaldehyde. This is the prime reason for recommending that the fish NOT be net-caught, but captured by using a clear plastic bag, under water. The fish is not harmed and not exposed to the air. [NOTE: Don't confuse 'coating and skin loss' with the shedding of excess mucous (coating) caused by some diseases, like Brooklynellosis. In the case of Brook, the coating is still there, just excess is being sluffed off.]
Fish being treated should not been recently fed. They should be in good health 'otherwise' (I know -- a judgment call). Finally, the treatment should be done under dim lighting and the QT kept with dim lighting in between treatments.
When Formalin is added to sea water, it removes oxygen by reacting with the dissolved oxygen in the water. Thus, to get oxygen back into the water, this treatment requires the use of a an airstone. Try to understand the basics here – The airstone doesn’t put oxygen into the water. What an airstone does is move the water at the surface so that the water can exchange gases (pick up oxygen). Thus the treatment is done in a rigid container (not a bag) with a large surface area and an airstone driven by a simple, small diaphragm pump. Also for this reason, the temperature must be controlled (see below).
In the presence of Formaldehyde oxygen is restricted in the way by the temperature of the water. This is one case where temperature is very important to be sure enough oxygen is in the water. The higher the temperature the less dissolved oxygen even with proper mixing. Controlling the temperature is essential to a proper treatment. The temperature must not exceed 80F at anytime. The reader must not take this control lightly. Let the temperature go up out of control and you’ll have a healthy, but dead fish!
Formaldehyde chemical activity is affected by pH. Maintain pH between 8.0 and 8.4 during treatment and in the quarantine tank.
These directions are given for those who begin by using Formalin (37% Formaldehyde). Formalin may be a challenge to obtain. It used to be applied to human wounds decades ago, but it has been replaced by other wound treatments. It is a strong disinfectant. However the dangers it poses has led to its limited availability. It is a human carcinogen and must be handled properly and with respect. Your 'friendly' pharmacist may order some for you. Just make it clear you understand its dangers, how little you need, that it will be disposed of properly (see below) and why you need it. However, if you search the Internet and some other places, you should be able to still find it. [DON'T buy too much. It won't store well.] At your local fish store (LFS) there may products on the shelf that contain Formaldehyde BUT in lower percentages. Read what percentage Formaldehyde is in the product. You can use these products if you remember to increase the amount you use to achieve the final Formaldehyde content of the treatment water. Unfortunately, there is no law regarding the names for such products. The product at your LFS may actually contain the word Formalin in its name, but isn’t actually the 37% Formaldehyde Formalin. Read the label carefully and closely.
Because of the carcinogen nature of this chemical, use gloves and safety glasses. Also, the disposal of such chemicals down the drain may be prohibited in your community. Check regulations and follow the proper disposal requirements for the used baths and any left over Formalin.
The final concentration in the treatment bath is:
1 ml of Formalin to every gallon of treatment water; or
250 ppm Formalin in the treatment water; or
0.01 % Formaldehyde gas
So, if you can’t obtain Formalin (37%) but can find a product that contains 3% Formaldehyde in water, then you have to add:
37 ÷ 3 = 12.3 times more of the product. In this example, the bath would be made up of 12.3 ml of this product for each gallon of salt water.
Measurements must be done carefully. DO NOT COUNT DROPS. Drops vary in size too much. The proper amount of Formalin must be accurately measured.
This treatment is used to cure marine fishes of Brooklynellosis. However it is also used to treat fishes of several other kinds of pathogens and surface parasites. I won’t list them all here. Regardless of the ailment, if you are instructed to perform a Formalin treatment, this is the process to use. Reader should note that I do this on all newly acquired Anemonefishes. This is a prophylactic treatment I perform on those fishes since they are so susceptible to Brook. I treat these fishes 3 times.
The marine fish should be given no less than 3 treatments of this process, every other day. I put diseased fishes through 5 treatments. No more are needed nor ‘better.’ Each treatment lasts 45 minutes, but can extend up to 60 minutes BUT NO LONGER THAN 60 MINUTES.
Ready to get to it?
EQUIPMENT
All equipment should be sized for the fish and for the purpose of its intended use. That is, don’t use a turkey baster to measure 1 ml.
Use clean equipment. After rinsing a few times in tap water, rinse many more times in pure, distilled water. Let all equipment go bone dry in between treatments.
Rigid treatment container (bucket, beaker, etc.) to suit the size of the fish (1 gallon or more per 4" of fish)
Small diaphragm pump
Adequate air line (I prefer the flexible nylon type rather than the standard plastic, but either is fine)
New (never used) airstone, soaked in pure water, then run in pure water for a few minutes before first use
Thermometer
pH meter (field, hand-held model or similar that will show pH in 0.05 units or better)
Fish to be treated is alone, in a quarantine tank (QT) with airstone or an air-driven corner biological filter
Formalin (fresh) [or a Formaldehyde containing water-based solution]
Measuring device for Formalin (pipette, burette, graduated cylinder, or marked dropper of the correct size for accurate Formalin measurement)
Capturing bag (instead of capturing fish in net, try to use a plastic bag)
pH and temperature adjusting chemicals and tools
Gloves
Safety glasses
Timer
Towels and clean-up materials
PROCEDURE
1. Make sure the pH and temperature of the QT water is in the preferred zone (see below)
2. 2/3 Fill treatment container with water from QT.
3. Check and adjust temperature to below 80F. Hold it steady. If temperature is too high, chill it a little, by sitting it on a bed of ice.
4. Put on gloves and safety glasses.
5. Measure 1 ml of Formalin for every gallon of bath water.
6. Mix-aerate with airstone for 2 hours
7. Check pH and be sure it is between 8.0 and 8.4
8. Dim the lights
9. Capture fish in bag, drain excess QT water from bag, and let fish slip into bath with airstone running. (BEST to put only 1 fish through this at a time because of the shortness of available oxygen. Don't treat multiple fishes at the same time. BUT you may treat one fish immediately after another in the same bath, providing bath is controlled as noted)
. Start timer
10. Monitor fish closely. If fish stresses, it may still be okay. If you fear fish is dying, then abandon the treatment.
11. Leave fish in bath for 45 minutes (i.e. treat for 45 minutes)
12. Capture fish under water in bag
13. Return to QT (make sure there is another airstone in QT running OR a corner sponge bio filter running by air and circulating the water in the QT.
14. Monitor fish
15. On the second day after treatment, repeat the process starting with 1. and using fresh/new treatment bath. This will be the second treatment.
16. On the second day after this second treatment, treat fish again, starting at 1.
17. Repeat pattern (treating every other day) until fish has had 5 such treatments (but no less than 3 total).
18. Hold fish in quarantine for no less than 4 more weeks for observation to verify treatment has been successful.
19. Dispose of all bath water properly.
20. When fish is deemed cured, throw away airstone and tubing.
THE END
If the fish isn’t cured, yet it was surely treated properly with fresh Formalin, then the ailment was not one of those affected by Formaldehyde.
I cannot stress the importance of controlling temperature, circulation, and pH.
I do not recommend the use of this chemical with any other medication. There are exceptions, but I don't like complicating treatments. However, the QT can be copper medicated with Cupramine and the fish still given Formaldehyde baths. Also, the QT can be administered antibiotics of certain types (Maracyn, Neomycin, Nitrofurazone, etc.) while the fish goes through this series of treatments. BUT, under no circumstances should fishes in a hyposaline solution be given Formaldehyde baths.
If the disease or condition is cause by parasites other than those that cause Brooklynellosis, an antibiotic treatment in the QT water may be wise in order to prevent a secondary infection from the sites that the parasites have abandoned.
The process is not particularly stressful to the fish, but can be to the hobbyist.
Anything new and for the first time can be intimidating. Post your questions or concerns. I’ve tried to provide the necessary details to answer most questions I could think of, however. . . I have tried to also provide the reasoning behind the procedure and recommendations.
I hope you and your fish thrive!
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