Stage 1-3 pre-filter replacement (every 6-12 months)
The three pre-filter stages use standard 2 x 10-inch threaded cartridges. Stage 1 (PP sediment, 5-micron): replace every 6 months in sediment-heavy water; 12 months in clear municipal water. Stage 2 (GAC carbon): replace every 12 months. Stage 3 (CTO carbon block): replace every 12 months. iSpring branded replacements: FPH5 (Stage 1), GAC-25 (Stage 2), CTO-25 (Stage 3). Third-party alternatives with standard 2 x 10-inch thread: Pentek P5-25, Pentek GAC-BIG, Pentek CTO-20 -- typically $5-10 each vs $10-15 for iSpring branded replacements. Replacement procedure: turn off supply valve, depressurize the system by opening the faucet tap until flow stops, use the filter wrench to unscrew each housing, swap the cartridge, and reinstall. Re-open supply and run for 5 minutes to re-pressurize.
Stage 4 RO membrane replacement (every 24-36 months)
The iSpring RCC7 uses a standard 75 GPD residential RO membrane (4 x 12-inch format). iSpring branded replacement: EWM-75G. Third-party compatible (standard FILMTEC 75 GPD format): Dow/Filmtec TW30-1812-75, Hydranautics ESPA2-4040, or generic 75 GPD FILMTEC-format membranes available from $25-50. Test membrane performance with a TDS meter: source TDS x 0.05-0.10 = expected output TDS range at 90-95% rejection. If output TDS exceeds 15% of source TDS, the membrane is degraded and should be replaced. Membrane replacement requires unscrewing the membrane housing (separate from the pre-filter housings), pulling out the spent membrane, and inserting the replacement.
Tank maintenance and pressure check
The iSpring 3.2-gallon pressurized tank maintains water under 7-8 PSI when empty. Check the tank pre-charge pressure annually using a tire gauge on the Schrader valve (close the supply valve and draw all water from the tank first before checking pressure). If pre-charge pressure drops below 5 PSI, add air using a bicycle pump -- the tank is designed for periodic air pressure top-up. Do not exceed 10 PSI pre-charge -- over-pressurized tanks reduce effective storage volume and can shorten bladder life.