These Aqua-Tech Ez-Change Replacement Filter Cartridges help ensure a cleaner tank, which means happier and healthier fish for you. You can use these in Starfish and Hex 5 filtration systems and aquariums. They use generous amounts of carbon to remove toxins and odors from your system. The high-density floss covering of the Aqua-Tech filter cartridge removes particulates and provides a safe and healthy environment for your fish. They are easy to use: simply remove and discard the old cartridge and replace it with one of these pre-assembled ones.