Part Replacement Logic

When to Replace the RO Membrane vs. Pre-Filters

Do not replace an expensive RO membrane just because water flow feels slow. Flow rate and TDS rejection point to different parts of the system.

Figure 5 — Flow vs. Rejection Decision Matrix: Measure both faucet stream behavior and pre-mineral TDS before ordering a new RO membrane.

Two Common Traps When Replacing an RO Membrane

Unseated membrane after DIY swap: If you just installed a brand-new membrane and TDS still reads high, open the housing and check that the two small O-rings on the stem and the flared brine seal are intact, lightly lubricated with food-grade silicone grease, and pushed all the way into the internal socket.
Reusing exhausted carbon pre-filters: Municipal water contains free chlorine or chloramines. If an overdue carbon block lets chlorine reach a new polyamide TFC membrane, it oxidizes the membrane pores—causing rejection to plummet while flow ironically looks faster.