EHEIM"s Coarse Blue Filter Pad is used as a parting layer between the mechanical (EHFIMECH) and biological filter medium (EHFISUBSTRAT/EHFISUBSTRAT PRO), Coarser particles are restrained and are thus removed from the water prior to entry into the biologically acting filter layers, This filter material may be rinsed and re-used; rinse in tank water or dechlorinated tap water to keep it"s biological filtering capabilities, SKU: RPS12358