Aqua-Tech EZ Change #3 Filter Cartridge pack is a replacement pack for Aqua-Tech 20-40 and 30-60 Power Filters for aquariums (sold separately). With Premium Activated Carbon that works twice as fast and works longer than other carbons, Aqua-Tech Filter Cartridges are an essential part of an effective filtration system for a cleaner aquarium. They trap more dirt, remove more impurities and deliver maximum water-to-carbon contact to make your aquarium water sparkle. These cartridges are pre-assembled and slide easily into place. Aqua-Tech Power Filters provide complete 3-stage filtration, providing coarse floss to remove large particles from aquarium water; carbon filtration to remove odors, discoloration and impurities; and a Bio-Tech Biological Grid to remove toxic ammonia and nitrit's. To ensure crystal clear aquarium water, change the filter cartridge once a month, as carbon deactivates with use. The amount of filtration needed to maintain an aquarium depends on a number of variables. These include tank size, individual maintenance habits and fish population. Whatever your individual needs, Aqua-Tech products help make aquarium maintenance simple and beautiful aquatic environment.