Aqueon Replacement Filter Cartridges are dual-sided, featuring dense-floss with over 25% more activated carbon than the leading brands. These patented cartridges were designed to ensure even distribution of activated carbon. To use, simply rinse under cold water and easily install using the "FRONT" orientation tab. Aqueon Replacement Cartridges are available in: Small, Medium and Large. Replace cartridges every 4 weeks for optimal performance. Cartridge contains high quality activated carbon that keeps water clean Installs in seconds: rinse first and align cartridge bottom key slot for an accurate fit inside the Filter Easy installation using the "FRONT" orientation tab For optimal performance, change approximately every 4 weeks Cartridges are Available in 3 sizes: Small: Fits Aqueon QuietFlow Filter: E Internal Power Filter Size 10 and MiniBow Aquarium Filters Size 1, 2.5 and 5 Medium: Fits Aqueon QuietFlow Filter: LED PRO Power Filter Size 10, Power Filter Size 10 and E Internal Power Filter Size 20 Large: Fits Aqueon QuietFlow Filter: LED PRO Size 20, 30, 50 and 75, Power Filter Size 20, 30, 50, 55/75, E Internal Size 40, Canister Filter Size 200, 300 and 400