The Penn-Plax Cascade Aquarium Filt-A-Pack is a filter bag that's filled with carbon and comes ready to use. The Pro-Carb lab-quality activated carbon also contains Pro-Z, zeolite crystals that helps remove ammonia. Together, they help promote a cleaner and clearer aquarium for your underwater buddies. Every purchase comes with 2, 8 oz. packs that are designed to fit inside Cascade canister filters. When you're all done simply dispose of the filter bag.