A-226 Fluval 404 Foam Filter Block   Fluval 404 Foam Filter Block 2 pieces per display pack Fluval Foam Inserts capture large particles for effective mechanical filtration, the crucial first stage in the filtration process. Custom fit to prevent bypass, they have a pore size that allows efficient water flow with less clogging for long-lasting filtration. These inserts also enhance biological filtration. For freshwater and marine environments. The photographic product images on this web site may not exactly reflect the product. Design revisions and color variations may exist.