The Marineland Penguin Filter Cartridges are preassembled and filter water through a double thick polyfiber pad that traps more waste and dirt particles than conventional filter cartridges. The cartridge is packed with super-efficient pure Magnum Activated Carbon, so it keeps working long after most carbons stop to absorb harmful pollutants which discolor aquarium water and cause unwanted odors. It's better than a separate bag. The patented ribbed back design evenly distributes carbon for maximum water-to-carbon contact. No "tea bag" effect...just crystal clear, crystal clean water. Performs mechanical and chemical filtration.