Aqua Gold from National Fish Pharmaceuticals. Nitrifying enzymes in a dry form which are activated upon its introduction into water. Crucial in all aquarium systems, for maintaining health and preventing disease. Can be used to enhance an already established biological filter, or it can be used to restore a filter that has been damaged by medications. Works in freshwater and marine aquariums and Koi ponds. Enough to treat 570 gallons 1 time.