Hey Mark, reading thru this thread I notice a couple of things that raised questions for me. You mention your source TDS is 125-135 and your RO output with that is typically 8. Any idea what water source you're on? Kal Lake or Duteau Creek?
Generally I'm on the Kal Lake source which gives me TDS readings of 210 or a bit higher. This can be corroborated by the RDNO water reports which list TDS as 234 from the Kal Lake intake. Earlier this year they temporarily switched South Vernon to the Duteau source due to turbidity from Kal Lake (used to be Duteau suffered more from this). The new Duteau treatment facility is evidently worth the money since that was giving me 35 TDS source! I actually started a thread on here to advise Vernon reef keepers so they could run their systems while on the low TDS source. I certainly took advantage & filled up all my RODI containers during that spell.
Nevertheless, with my 75 gpd membrane system on the Kal Lake 210 TDS source, I can get the TDS after RO down to 1 within about 5 to 10 minutes of running it. During the winter with colder input water I actually get a 0 TDS reading. Makes me think you should be getting better than 8 TDS from a 135 TDS source with your membrane. Could be that my TDS meters are out of whack, but I've only recently had to change my DI resin after over 3 years of use (2390 gals produced), so that should be a good indication that my RO output has very low TDS. Food for thought?
With regard to pressure issues, I've adjusted the PRV in my house plumbing to provide at least 80 psi downstream. I also have two pressure gauges to monitor my RODI system. One at the input shows house pressure, one after the pre filters, before the membrane. This allows me to monitor the difference & is a great indicator that one or more of the pre filters needs service.
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