Phos Zorb is a specialized filtration medium in a convenient pouch that eliminates cloudy water caused by phosphate and silicate. Phos-Zorb removes these common nutrients and enhances the growth of hard and soft corals in saltwater. Phos-Zorb also removes compounds that inhibit plant growth in freshwater aquariums. Safe for all fish, invertebrates and planted aquariums. Contains 1 large pouch for up to 55 gallons aquariums. Replace every 2 months. Shipping weight: 1/2 lb.