Top Fin Aquarium Filter Cartridges provide balanced three-way filtration to keep water clear and fish healthy; mechanical, chemical and biological. Only at PetSmart. Features: Effective three-way filtration helps keep water clear Includes: 12 PK Unassembled Cartridge, 12 Filter Bags, 12 Activated Carbon Packets, 1 Filter Frame and Clip Water Type: Freshwater Filter Type: Large Unassembled Cartridge Dimensions: Filter Cartridge is approximately 4.5 inches wide and 6.75 inches high Compatible With: Top Fin Aquarium Power Filter Top Fin 20 Gallon Aquarium Starter Kit Instructions: 1. Detach the clip from the filter frame and slip a filter bag over the frame. 2. Pour one pre-measured packet of Activated Filter Carbon into the filter bag. 3. Fold the flaps on the filter frame down over the top of the filter bag and press the clip over the "H" shaped tracks in the center of the flaps. Gently shake the filter cartridge to settle the carbon. 4. Rinse the filter cartridge under cool tap water to remove dust. 5. Using two hands, carefully insert the filter cartridge into the "V" shaped slots on the sides of your power filter's filter chamber. Ensure that the filter cartridge is completely seated all the way down into the filter chamber. 6. Change filter cartridge every 3-4 weeks for clean water and healthy fish. Size: Large.