Bio-chem Zorb removes synthetic chemicals, natural organic pollutants, and metabolic by-products in aquarium water. This product is composed of a blend of 2 organic scavenger resins, 2 ion-exchange resins, and a high porosity activated carbon in a 6 1/2" x 6 1/2" pouch. One pouch treats 55 gallons. Place pouch above foam filter pads in any FilStar canister filter. Replace pouches every 1-3 months.