Microline reverse osmosis systems replacement filters cartridges-Set of 2 replacement filters, this system uses sediment pre-filter to reduce sediment particles before the amembrane filters out impurities larger than .001 microns ( Not includedin this set ). The GAC post filter treats for taste and odor. You can find and order all your filters at once if you are looking for the reverse osmosis membrane to be added to this set. Stage 1 – Sediment Pre-Filter (S7011) – Replace Every 12 Months Stage 2 – RO Membrane CTA 35-50 GPD (S1224RS) – Replace Every 24 months (Not included in this set) Stage 3 – Carbon GAC Post Filter (S7025) – Replace Every 12 Months