|The Nitra-Zorb cartridge for the Nexx and SmartFilter is the first water filtration medium that removes ammonia, nitrite and nitrate in freshwater aquariums. Nitra-Zorb is a blend of natural and synthetic ion-exchange resins that selectively removes ammonia, nitrite and nitrate. Use Nitra-Zorb in your Nexx or SmartFilter when setting up new aquariums. NitraZorb controls the level of toxic ammonia and nitrite during the initial development of the biological filter. In established aquariums, Nitra-Zorb helps control sudden spikes in ammonia and nitrite from the addition of new fish or anytime ammonia or nitrite is detected.