Fluval SPEC Replacement Foam Filter Block (3 Pack) Foam filter block designed for the Fluval Spec aquarium Traps particles and debris Easy to replace Specifically designed for Fluval Spec Aquariums, the Fluval Spec Foam Pad effectively removes large particles and debris from your aquarium for effective mechanical filtration. Although the primary purpose of Fluval Spec Foam Pad is mechanical filtration, biological activity will eventually occur within its pore structure. It is the perfect size to allow efficient water flow with less clogging.