Penn Plax Cascade Pro-Carb Canister Filter for Aquariums, 8 Total Filters (4 packs with 2 filters in each pack) 8 Total Filters (4 packs with 2 filters in each pack) Convenient, ready-to-use filter bags for use with your Cascade cannister filter Contains carbon & ammonia removing zeolite crystals Filter media fully enclosed in a disposable nylon-mesh bag