Fluval Nano Filter Bio-Foam. Specifically designed to fit inside the Fluval Nano Filter, Fluval Bio-Foam captures debris for effective mechanical filtration. 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. Key Features : Specifically designed to fit inside Fluval Nano Filter Captures debris for effective mechanical filtration Large surface areas encourage the proliferation of friendly nitrifying bacteria Provides efficient biological filtration Fits perfectly inside the filter chamber to prevent debris bypass Ideal pore size allows efficient water flow, less clogging and long-lasting filtration Suitable for freshwater environments.