Malachite Green

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Malachite green
Common Name(s): Aniline green
Molecular Formula: C23H25ClN2
Used For: Parasites, fungal and bacterial infections
Caution: Avoid eye contact
Material Safety Data Sheet: Malachite green


Malachite green has traditionally been utilised as a dye, having an intense green colour. It is predominately used in freshwater aquaria, as it works well as a treatment for freshwater mould that effects eggs in aquaculture (Sprolegnia) and freshwater ichthyophthirius (Freshwater Ich, which is distinct to marine ich, Cryptocaryon).

Care must be taken with its use as it is a respiratory poison, teratogen and carcinogen. Accumulates in tissues, more toxic at lower pH, phytotoxic and inactivated by light therefore aquariums need to be kept dark. It is also toxic to fish eggs, young fish (with reports it is also toxic to small marine fish), invertebrates and algae. [1]

When diluted to an appropriate level, can be used to treat fungal infections, bacterial infections, and various parasites in fish and on fish eggs. [1] It is preferable to use other treatments if possible, since the concentration of malachite green cannot be measured by the average hobbyist, significantly increasing the risk of fatal over dosing.

One of the active ingredients in Vertonex and Protomarin Coral.


Should be utilised in a separate quarantine tank, as it will absorb into most surfaces, particularly silicone. [1] Additionally it is inactivated by light, therefore the treatment aquarium should be kept dark.

Gloves and goggles should be used when handling.



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