This product is a topical antifungal medication that can be applied to all types of fish. It is especially useful for treating aquariums with a high water flow and for spot treatments on larger fish. The Methylene Blue formula includes a powerful fungicide that prevents the growth of any type of fungus, including those that cause white or black gills. This also helps prevent the spread of any infection to other fish in the tank. Don’t miss out on this great product!