The Hagen A291 fits the following filters:
The A291 Marina Slim Filter Carbon Cartridge - 3-Pack arrives in a convenient three pack and fits the S10, S15, and S20 Slim Filters from Marina. The Marina Slim filter insert utilizes activated carbon technology and Ceramitek to make your aquarium healthy. The Marina Carbon Filter removes pollutants, ammonia, and odors, while also enacting biological filtration, to ease stress on fish. This aquarium carbon filter is easy to use and is best suited for tropical fish.
A291 Marina Slim Filter Carbon Cartridge - 3-Pack specifications: