Penn-Plax Cascade 300 Filter with Internal Replacement Cartridge, 6 Total Cartridges (3 Packs with 2 cartridges per Pack);

Cascade filter replacement cartridges from Penn-Plax work to keep your aquarium water clean & clear. Each pack contains 2 disposable filters specially designed to fit your Cascade 300 internal power filter. Each filter uses activated carbon to remove ammonia & nitrites keeping your aquarium clean & healthy. Each easy-to-replace disposable cartridge is perfectly sized to fit your Cascade 300 internal power filter. Intact used cartridges can often be rinsed and refilled with activated carbon of your choice. For use on Cascade 300 internal power filters only.