High performance filter medium for mechanical filtration The innovative, patented 3D fiber structure of sera pond crystal clear Professional very quickly removes even smallest particles above 10 µm (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. Maximum filter performance can be achieved by combination with a UV-C lamp and/or coagulants such as sera phosvec•clear.