R.O. Replacement Carbon Cartridge from D-D aquatics but it will fit any 10″ reverse osmosis unit. It is hard to know exactly when it needs to changed but as a guide every 6 months. For a more exact timescale you can check the quality of the water after each stage with a TDS meter. This 10 inch R.O. carbon cartridge is of the highest quality. 10 micron carbon cartridge R.O replacement carbon cartridge
