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: X-Small, Small, Medium and Large. Replace cartridges every 4 weeks for optimal performance. Features: 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 FilterEasy installation using the "FRONT" orientation tab For optimal performance, change approximately every 4 weeks Fits Aqueon QuietFlow Filter: E Internal Power Filter Size 3 Includes: 3 Replacement Filter Cartridges Intended Pet(s): Fish Material(s): Dense-floss and Activated Carbon Product Dimensions: 2.25 X 0.50 X 3.25 Instructions: Remove used cartridge from Bio-Holster grid by pushing down gently on the holster and pulling the tab on the cartridge upwards. Discard used cartridge. Bio-Holster grid should not be removed or cleaned, as it contains beneficial bacteria. Rinse new cartridge under cold water to remove carbon dust. Insert new cartridge into Bio-Holster grid by aligning the key slot in the cartridge with key slot on the biological grid. For optimal performance, change approximately every 4 weeks. Aqueon Replacement Aquarium Tank Filter Cartridges, Size: 3 Count | PetSmart