Aquarium Pharmaceuticals (API) Nitra-Zorb filtration media is a ready-to-use pouch that can be added to your filter to remove ammonia, nitrite, and nitrate. Nitra-Zorb filtration media is made of natural and synthetic ion-exchange resins that selectively remove toxins from freshwater aquariums. Nitra-Zorb filtration media is completely phosphate-free and can be reused after recharging.