Nitra Zorb is a blend of natural synthetic ion-exchange resins that remove ammonia, nitrite and nitrate in freshwater aquariums. When used in new aquariums, Nitra-Zorb controls the level of toxic ammonia and nitrite during the initial development of the biological filter. In established aquariums, it helps control sudden surges in ammonia and nitrite caused by the addition of new fish, or anytime ammonia or nitrite is detected. Comes in a fully rechargeable 6 1/2" x 6 1/2" pouch. One pouch treats 55 gallons.