API Bio-Chem Zorb Filter Media Pouch Contains eighteen (18) API BIO-CHEM ZORB SIZE 6 Aquarium Canister Filter Filtration Pouch 18-Count Bag Cleans and clears aquarium water removing aquarium pollutants, including colors, odors, heavy metals, and toxic gases which cloud water and degrade water quality. Contains a unique superior resin-carbon blend that removes compounds 3x more effectively than carbon alone. Easy-to-use pre-dosed pouch fits most canister filters on the market for freshwater, saltwater and reef aquariums. Use when starting or maintaining an aquarium, replace every 2 months or sooner if aquarium is heavily stock and/or colors and odors are detected