Overview Emperor Filter Cartridges provide supreme mechanical and biological aquarium filtration in both freshwater and saltwater aquariums. The preassembled Emperor Filter Cartridges are made of double-thick polyfiber, to trap more waste and dirt particles. Filters aquarium water through a 44-square inch filter pad. Inside each disposable filter cartridge is 2 full ounces of Black Diamond Activated Carbon. The patented ribbed back design ensures maximum aquarium water-to-carbon contact. It works longer and faster to absorb harmful pollutants which discolor aquarium water and cause odors. It's better than a filter bag: just shake and rinse. There’s no tea bag effect, just crystal clear, clean aquarium water. Designed for both the Emperor 280 Filter and Emperor 400 Filter.