Exclusively designed for Fluval aquarium canister filters, Fluval Bio-Foam performs exceptional mechanical and biological filtration. Bio-Foam\'s dense structure is very effective at trapping small particles that are not captured in the first stage of foam filtration. In addition, its intricate network of pores provides a large surface area that encourages the growth of helpful nitrifying bacteria, which is crucial for efficient biological filtration and goes a long way in creating clear and healthy water for fish and plants to thrive. Suitable for freshwater and marine environments. 2-pack.For Fluval Filter Models: 304, 305, 306, 404, 405, 406