Specifically designed to fit inside the Fluval® Nano Filter, the Fluval® Bio-Foam captures debris for effective mechanical filtration, plus it has large surface areas that encourage the proliferation of friendly nitrifying bacteria, which provide efficient biological filtration. Custom-sized, it fits perfectly inside the filter chamber to prevent debris bypass. Bio-Foam has a pore size that allows efficient water flow, less clogging and long-lasting filtration. It is suitable for freshwater environments.