API Nitra-Zorb Filter Media Pouch Contains one (1) API NITRA-ZORB SIZE 6 Aquarium Canister Filter Filtration Pouch 1-Count Bag Removes toxins that can be harmful to fish and lead to algae growth. Removes ammonia, nitrite, and nitrate from aquarium water. Easy-to-use pre-dosed pouch fits most canister filters on the market, for use in freshwater aquariums Use when starting a new aquarium and when ammonia or nitrite is detected, replace every 2 months.