API Crystal BIO-Chem ZORB Size 10 Aquarium Filtration Media Cartridges Contains one (1) API CRYSTAL BIO-CHEM ZORB SIZE 4 Aquarium Filtration Media Cartridges for API NEXX filters 4-Count Box Cleans and clears aquarium water removing debris and 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 cartridge fits canister filters API NEXX, 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