Copper Power Methylene Blue is effective against superficial fungal infections of fish. 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. Can be used for both saltwater and freshwater fish. WARNING Should be used in separate treatment/hospital tank with non-porous surfaces to avoid staining or retaining of medication.