Aqueon Replacement Filter Cartridges Easy Install Dual-Sided Carbon Filter Media Small 6-PackThese unique cartridges were designed to ensure even distribution of carbon throughout for more thorough filtration and longer cartridge life. Features: High quality activated carbon keeps water clean Align cartridge bottom key slot for an accurate fit inside the filter Rinse under water to remove carbon dust before replacing For optimal performance, change approximately every 4 to 6 weeks Do not clean Bioholster when replacing the cartridge as it