Culligan AC-50 & LC-50 Aqua Cleer RO Compatible Filter KitFilter Replacement Kit for Culligan AC 50 & LC 50 Aqua Cleer Reverse Osmosis Systems (RO Membrane Sold Separately) INCLUDES: STAGE 1 1x Sediment Pre Filter (RS 23 SED5) Replace every 6 12 months or as needed STAGE 2 1x Carbon Block Pre Filter (32 175 050 100) Replace every 6 12 months or as needed STAGE 3 0x DISCONTINUED (RO Membrane 1224437) Replace every 24 months Recommend converting system with the PuROTwist PT4000T50 SS RK for continued use STAGE