Aqueon Replacement Filter Cartridges for E Internal Power Filters feature a patented, dual-sided dense-floss design and contain over 25% more activated carbon than competing brands. These cartridges provide even carbon distribution for more thorough filtration and longer effectiveness.X-Small cartridges for Aqueon E Internal Power FiltersPatented design with over 25% more premium activated carbon than other leading brandsEven carbon distribution ensures thorough filtration and longer cartridge lifeDirections: For optimal performance, change cartridge approximately every 4-6 weeks. Rinse under water to remove carbon dust before replacing. Align cartridge bottom key slot for an accurate fit inside the filter. Do not clean Bioholster when replacing the cartridge as it contains beneficial biological bacteria.Dimensions: 5.24"L x 5.7"H x 1.75"D