Bio Chem Zorb is a specialized filtration medium in a convenient pouch that removes organic aquarium pollutants, including colors, odors, heavy metals and toxic gases as well as other compounds that carbon alone cannot remove. Bio-Chem Zorb also removes light blocking impurities for improved growth of corals in saltwater and plants in freshwater aquariums. Contains 1 large pouch for up to 55 gallons aquariums. Fits most filters. Replace every 2 months. Shipping weight: 1/2 lb.