Another Great Product From The Fluval Spares Range. Fluval Foam Inserts capture large particles for effective mechanical filtration of your Fluval Aquarium, the crucial first stage in the filtration process. Custom fit to prevent bypass, they have a pore sizethat allows efficient water flow with less clogging for long-lasting filtration. Theseinserts also enhance biological filtration. For freshwater and marine environments. 2 per pack.