Good to use for both fresh and saltwater aquariums Ready to use bags, convenient use for all types of filters. The ceramic material that the ceramic rings is made of is porous. Ceramic ring size: 1/2 "x 1/2 ", Contain: 4 lbs Comes with 4 Pcs zip mesh bag Aquarium Premier Bulk Bio Ceramic Rings Filter Media For Fresh Water, Sea Water Fish Tank Canister Filter,Koi Fish Pond Reef Filter