Patented dual-sided dense-floss cartridges contain over 25% more activated carbon than the leading brands. These unique cartridges were designed to ensure even distribution of carbon throughout for more thorough filtration and longer cartridge life. Fits Aqueon E Internal 10 gallon and MiniBow filters Ready-to-use cartridge contains high quality activated carbon that keeps water clean Installs in seconds: align cartridge bottom key slot for an accurate fit inside the filter For optimal performance, change approximately every 4 to 6 weeks Do not clean Bioholster when replacing the cartridge as it contains beneficial biological bacteria