These foam blocks and inserts were made to fit specific aquarium filter models (you can also shop by brand). Foam blocks and inserts function as biological and mechanical filter media (for more foam media check our mechanical media; we also have stand-alone sponge filters). If you plan to use foam for your primary biological media, make sure you use something else as your primary mechanical filter media (another sponge works) so that you're filtering out large particles before they clog your bacterial bed.
