Eheim Substrat (formerly Ehfisubstrat) is a bio filter medium with high biological performance. Eheim Substrat is a highly porous filter medium made from specially-designed sintered glass with an enormous surface area of 450 mper liter, thus biologically filtering the water. The surface structure of Eheim Substrat offers excellent colonisation conditions to the important purification bacteria. When changing the filter material, mix about 1/3 of the used medium with new one to achieve rapid repopulation of bacteria. Eheim Substrat may be washed with lukewarm water and be used several times. Before use rinse thoroughly. To be used in fresh and marine water.Eheim Substrat is available in different packing sizes:-1 L carton-2 L carton-5 L carton