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. Fits eheim calssic 150 or 2211 filter.