JBL UniBloc is a set of two high-quality foam pads of medium-pore size for effective biological filtering. The pads provide optimum colonisation conditions for cleansing bacteria. The JBL UniBloc padshave a section which can be removed to be replaced with filter material to treat special problems. Package content: 2 foam pads, blue, 20 ppi suitable for the JBL external filter CristalProfi e1500, e1501, e1901 as well as e1502 and e1902JBL recommendation:- Cleaning approx. Every 6 months- Replace after cleaning two or three times- Only one of the two pads should ever be cleaned or replaced each time, alternately.