Biological high performnce filter open pored, three-dimensional structure, the sintered glass tubes made or recycled glass provide a surface that is proven to be optimal for the settling of useful filter bacteria .One liter of siporax provides as much settling area as, for instane, 34 litres pf ceramic and ensures more than 200 litres of crystal clear , biologically clean water . Suitable for quick and slow filters as well as all internal and external filters.