Kordon Methylene Blue is effective against superficial fungal infections of fishes. The drug may be used as an alternative to Malachite Green for the control of fungus when it is known that the fish to be treated are sensitive. Methylene Blue is safe for use with fish eggs and fry for the prevention of fungal infections. As a secondary use, it is effective against some external protozoans, such as Ichthyophthirius (Ich), Chilodonella and Costia. CAUTION: Methylene blue is toxic to plants and is harmful to biological filtration, preventing nitrification and resulting in a rapid rise in ammonia and/or nitrite levels. Treatments should be carried out in a separate hospital tank or other suitable container. Methylene blue can permanently color the silicone sealant in aquariums.