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Acriflavine is a yellow-orange powder that has been used for Koi heath treatments for many years. Until recently, Acriflavine has been viewed as not very effective and even described by some as a useless dye. It is however my opinion that more experimentation with Acriflavine is necessary to unlock the full potential that it has for the Koi industry.

What is currently common knowledge about Acriflavine is that it is an effective treatment against bacterial disease such as Flexibacter columnaris. It is also effective against some external parasitic infections such as Chilodonella, Hexamita, Ich and Oodinium. As a fungicide it is effective against Saprolegnia. Some claim it is the only effective treatment against dropsy, but I have never been able to cure a case of dropsy, even with the aid of injections.

Acriflavine is a very forgiving chemical that can be overdosed to some extent without apparent harm to fish, although there have been reports that it may sterilize fish. There have been some reports that Acriflavine may damage the slime coating or the mucus producing cells of fish, but at this stage there is inadequate evidence to support such a claim. The effect on the beneficial bacteria is not clear although one can expect it to “knock” the filter back for a short while. What makes the use of Acriflavine very attractive is that it can be safely employed in conjunction with salt, organophosphate, Methylene Blue, Malachite Green and antibiotics. It is common practice to use a salt and Acriflavine combination in quarantine facilities.

The mode of action is that Acriflavine bind with nucleic acids of the disease causing organisms. The pond-doctor also supports the use of Acriflavine when he states the following mode of action on viruses: It is absorbed through cell membranes where it reacts with DNA inside the cells. This disrupts the pathogen's ability to reproduce causing an accelerated death and preventing the spread of the infestation. It is still not clear why Acriflavine has this effect on DNA within cells.

I have also read Dr Eric Johnson’s book, “Koi Health and Disease” some time ago. He has tested Acriflavine on five groups of fish twice for the effect that it may have on Lymphocystis. Lymphocystis is a viral disease causing warty, rough areas on fish. It is not life threatening but very disfiguring. (See more information here). I have also done some experimenting and would recommend Acriflavine dips or topical treatment if you would like to have a shot at curing Lymphocystis lesions.

Directions for use.

Pond dosage.

Dose at 5 particles per million (ppm). That is 5 gram of Acriflavine powder per 1000 litres of pond water. No water changes are necessary and the yellow colour will disappear over time. It may impact on the effectiveness of the bio-filter and is detrimental to pond plants. If using Acriflavine solution obtained from a Koi dealer, follow the manufacturer’s instructions.

Short term bath/dip.

In a separate container with pond water and adequate aeration, prepare a 10 ppm solution by adding 10 milligram Acriflavine per litre. Place the affected fish in this container and return it to the pond after 2 hours. This treatment can be repeated after five days.

Topical treatment.

For topical treatment of either Lymphocystis viral lesions or bacterial ulcers, I normally prepare a paste using Acriflavine powder and surgical alcohol and apply directly to the affected area. This treatment is repeated if necessary on ulcers and every 3 to 5 days for 3 consecutive treatments on Lymphocystis lesions. If you cannot obtain Acriflavine in powdered form, use the stock solution from your Koi dealer without diluting it.


I have tried my utmost to determine how long will the active ingredients in Acriflavine remain in the water after dosage. My search up to now has yielded no results and one must assume that Acriflavine as a dye remains active in a pond, as long as the yellow colour remains in the water.

Last Updated on Wednesday, 29 February 2012 12:46