Cascade Bio-Rings Filt-A-Pack is a convenient ready-to-use nylon mesh filter bag filled with Ceramic Rings. Surface area and pores sized to accommodate bacteria necessary for biological balance and to remove toxic Ammonia and Nitrite. Produces crystal-clear water. For bulk use, mesh bag can be cut open for use in any Canister Filter. Can be used in Penn-Plax Cascade Canister Filter, Eheim ECCO, Eheim Pro & Pro II, Aquaclear 500, FilStar Canisters and Fluval Canisters. Shipping weight: 3/4 lb.