High performance filter medium for mechanical filtrationThe innovative patented 3D fiber structure of sera crystal clear Professional very quickly removes even smallest particles above 10 m (such as floating algae or sludge).Unlike common filter wool the filter balls keep their shape and can be washed out several times. They are 80% reusable after washing out.The high performance filter medium is suitable for both freshwater and marine aquariums and all filter types. The biological filter medium sera siporax Professional is the perfect addition to sera crystal clear Professional.