Keep your aquarium clean and healthy with the Penn-Plax Cascade 80 Filter Cartridge 4 pack Replacement. This filter cartridge is designed for external filter locations and is suitable for freshwater tanks up to 10 gallons. The pack includes 4 replacement cartridges, each ensuring efficient and safe filtration of your aquarium water. The Pen Plax Cascade 80 Filter Cartridge is suitable for use with the brand's external filter systems. It is important to regularly change the cartridge to maintain the cleanliness and health of your aquarium. This product can be found under the Filters, Fish & Aquariums, and Pet Supplies categories on eBay.