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.