Aqua Medic Anti Phos V 5000 ml Features: A highly effective substance made of iron in granular form to remove phosphates and silicates from freshwater and saltwater aquariums to combat unwanted algae growth. Anti Phos V (GFO) contains no aluminum and is completely non-toxic to plants and animals, making it very suitable for use in reef tanks. 500 grams can treat a naturally stocked aquarium for a period ranging from 3-6 months depending on the phosphate level. Anti Phos V can bind about 10 grams of phosphate per kilogram. Regularly check the phosphate level in the aquarium to determine if the material needs replacement.