API E.M. ERYTHROMYCIN powder helps broad spectrum treatment and control of bacterial disease, such as body slime, mouth fungus, Furunculosis (open lesions and swelling), bacterial gill disease and hemorrhagic septicemia (blood spots without sign of skin damage). For use in both freshwater and saltwater aquariums. Can be used with any API Ich, fungus or parasite remedy to help prevent secondary bacterial infection. This medication will not color the aquarium water.