API NITRA-ZORB SIZE 4, Natural and synthetic ion-exchange resins that selectively remove ammonia, nitrite, and nitrate from freshwater aquariums, Also helps during start up by reducing unhealthy ammonia surges while establishing the aquarium s ecosystem, Completely phosphate-free and can be reused after recharging, , UPC : 317163017760, Size : 2 PACK, Product Type : Aquatics - Filtration / Filter Inserts SKU: BC014079