This our replacement RO filter set for our ProSeries 4-Stage Reverse Osmosis System. Most reverse osmosis filter sets should be changed once per year. Depending on your water quality, filters generally get dirty and should be replaced in order to keep your membrane working properly, and keep cleaning contaminants out of your drinking water.  The membrane is not included with this set, however you can select it, it's recommended that you should change membrane every 3 years or sooner depending on your water quality. A sanitizer kit is also available as well. When you change your filters you should sanitize your systems before replacing them, to help keep the system clear of any harmful bacteria. Filter set includes: (1) 5 Micron Sediment Cartridge Filter(1) 10 Micron Carbon Block Cartridge Filter (1) 10" Inline GAC Cartridge Filter (1/4" Female with 2-3/8" fittings and 2-1/4" Fittings)