Nitra-Zorb Cartridges help facilitate a successful aquarium start up while reducing the risk of fish loss by preventing ammonia surges. Scientifically proven to remove ammonia and nitrite in new and existing aquariums, and to reduce nitrate. Additionally, the cartridge pads remove fine debris to provide effective mechanical filtration. Nitra-Zorb Cartridges are not only filled with superior media, but they are also densely filled to provide even more filtration capacity. Use when starting a new aquarium or whenever ammonia and nitrite are detected. Also use whenever nitrate tests above 20 ppm. Intended for freshwater applications.