Malachite Green + Formalin

Malachite Green and Formalin have been used for many years against a range of parasites, and can be used together or separately as anti-parasite treatments against Gyrodactylus  (skin flukes), Dactylogyrus  (gill flukes), Ichthyobodo  (Costia), Trichodina , Chilodonella and Ichthyophthirius (white spot). It is especially effective against white spot, because the relative long active life of this treatment, together with the low filter toxicity makes it ideal for tackling the complex life cycle of this protozoan parasite.

I am not qualified to explain in detail but what I understand is that Malachite Green acts as a respiratory poison to pathogens while Formalin is a powerful disinfectant used to kill microorganisms. Together they also have a mild anti-bacterial effect. In most circumstances Malachite Green and Formalin will not destroy biological filtration bacteria, but they may ‘knock the filter back’ for a short while, so regular checking of water parameters shortly after pond treatments are essential.

Please note that Malachite Green as well as Formalin should be handled carefully and contact with eyes and skin should be avoided.

Malachite Green and Formalin can be used separately for treatment, but are usually used together because of the synergistic effect during treatment. Together they are more effective than the sum of their separate individual capabilities.

Formalin

Formalin and Formaldehyde are essentially the same things. Formalin is Formaldehyde at a concentration of 37% in water. It’s not an easy mix to stabilize and sometimes Methanol is used to make it more stable. Formalin should be stored in the dark and above 40C to prevent the formation of Formaldehyde. You should never use Formalin that contains a white precipitate – this is the toxic Paraformaldehyde (I am currently doing a study in this regard). Formalin may be used as a parasite treatment on its own or in conjunction with Malachite Green. Formalin on its own can be used against protozoan and metazoan (multi-celled) parasites.

Dosage

For a bath treatment, 0.2 ml per litre of water in a separate container. You can keep this treatment up for a maximum of 60 minutes. If necessary, this treatment can be repeated for a maximum of three consecutive days. Formalin can irritate gills, so it should be avoided where gill disease is suspected. Make sure the water is aerated at all times, because formalin is an oxygen scavenger.

For a pond treatment, 0.02 ml per litre of water. If necessary, this treatment can be repeated every 4 days with a maximum of three consecutive treatments. Effect a partial water change between treatments. Again, do not treat with formalin where gill disease is suspected and aerate at all times.

Please note that formalin may kill already weak fish, it may harm the filter bacteria and the water needs to be oxygenated at all times.

Malachite Green

Malachite green has powerful anti-fungal properties and is used when fungus are present on fish or to protect fish-eggs from infection. When fungal infections are present on fish, this is normally a secondary infection and therefore the main problem, usually bacterial, should first be resolved. If the root cause of the infection is not resolved, the Malachite treatment may not be successful. Malachite Green is also effective against some parasites.

Malachite green may react in two ways, depending on the pH of the water. The initial strong green colour will prevail at pH below 7, while in water with a pH above 7 it soon becomes clear. In water with a pH above 7, it may therefore seem to disappear, but it is still present.

Use Malachite Green that is zinc-free. The Malachite Green powder is a very fine powder that will stain your skin and are reportedly Carcinogenic if a person is often expose to it. It is therefore frequently made up as a stock solution that is easier and safer to handle. To make a stock solution, mix 20 grams Malachite Green with a litre of distilled water. This gives 20 mg Malachite Green per one ml of stock solution. If this stock solution is kept in a dark area it will last indefinitely. The stock solution can be applied topically on lesions/fungus. The use of the stock solution for bath and pond treatments will be discussed under the dosage heading.

Dosage

For a bath treatment, use 2 mg per litre of water in a separate container, normally for 30 minutes. You can however keep this treatment up for a maximum of 60 minutes. If necessary, this treatment can be repeated for a maximum of four consecutive days. Because of the small volume of water, make sure the water is well aerated. If you prefer the stock solution, use one milliliter of stock solution for every 20 litres of water.

For a pond treatment, 0.2 mg Malachite Green is used per litre of water. If necessary, this treatment can be repeated every 3 days with a maximum of three consecutive treatments. I normally effect a partial water change between treatments. If you prefer the stock solution, use one milliliter of stock solution for every 200 litres of water.

Please note it is easy to overdose, because it is given in mg. The dosage per 1000 litre is therefore 0, 2 g

Sterilizing eggs. Malachite Green is also an excellent chemical to use in the prevention of fungus on fish eggs after spawning.

The Malachite powder are mixed in a separate container of water and distributed evenly in the hatching tank/pond. The formula is as follows:

Use 0,2mg of Malachite Green powder per one litre of tank/pond water. Please note it is easy to overdose, because it is given in mg. The dosage per 1000 litre is therefore 0,2 g. Do the treatment within a few hours after spawning, because if there are still Malachite Green present in the  water by the time the fry hatch, it may be fatal to them

Malachite Green and Formalin.

As stated earlier, the combined effectiveness of Malachite Green and Formalin is higher than the sum of the individual chemicals as described above. A combination of Malachite Green and Formalin is commonly known as the Leteux-Meyer mixture.

There are several variations to this mixture, but the mix that I normally use is 3.3 gram of Malachite Green, dissolved in one litre of Formalin. This mixture is then used in ponds at the rate of 50 ml per 3000 litres of pond water. This treatment can be repeated every 4 to 5 days for a maximum of 3 consecutive treatments, with a partial water change between treatments.

For stubborn cases, this mixture can sometimes be used as a bath at a dosage of 0.3 ml per 10 litres of water for a maximum of 60 minutes.

Points to remember.

Malachite green is de-activated by light, so when a pond is exposed to sunlight, it is advisable to treat in late afternoon and to switch the UV clarifier off.

This formula was not tested on any other species of fish. Only Koi.

Formalin should not be used where there may be existing gill damage or where skin ulcers are present.

Both Chemicals are reportedly carcinogenic and should be handled with care.

The effectiveness of Malachite Green and Formalin will differ in alkaline or acidic water, and it will be less effective in ponds with high levels of suspended solids, algae etc.

Last Updated on Wednesday, 22 October 2014 20:03

This article was compiled by Pieter Odendaal.

Thank you Pieter for allowing its use here.