RO/DI and TDS

PPBlimpy · Jun 1, 2026

Let me start by saying I know everyone wants Zero TDS.

Been running my tanks directly off my well @350+ tds for years

I have put together a Frankenstein of a RO/DI system and still have a lot of tuning ahead of me and need to replace the RO membrane with a 99%
20micron prefilter into two 3 stage sediment filters running in parrallel w/ 10m,5m,1m filters. plumbed back together to go into a single 3 pot Carbon
block. Current Carbon specs unknown and will be replacing soon with 1M CTO, 1M chlorine and voc and a .5m chlorine and voc.
After sediments and carbons it goes to a booster pump set at 90 psi to feed the RO membranes
After the RO I am currently seeing 14 tds
This includes a 50G C02 degassing tank that the RO goes into with air pump / stone, letting it bubble for 24 hours and then another pump to push thru the 3 pot DI saver.

I am still burning thru DI like crazy- specificly Anion DI.

I know I need to get the 14 lower prior to DI but really thinking of saying screw it and be happy with the 14 TDS and not run DI at all.

I made 75G of RODI and burned up the anion and the mixed bed completely. TDS was running at zero for that 75g but started creeping.

anyone run their tanks of water that is under 20 TDS?

I was / am happy with my tank running 350 tds so I can imagine it will hurt anything. What has got me going this route finally is a neighbor treating there well and causing devastating results in my tank because of chlorine or bleach in the water table.

Saltyreef · Jun 1, 2026

Have you tested for chlorine in your well water? You may need to run a smaller micron prefilter and carbon as your final stage.
Also, have you done any calcs for your rejection rate or product to waste ratio?
Whats your well pump pressure at before you are boosting?

I dont get my supply from a well but i have similar city tds as you with high chlorine and co2.
i run a 5 stage with .5 micron sediment, .5 micron carbon, spectraselect 99% membrane, silica buster DI and maxcap DI.
I degas for a day or 2 and my DI lasts for a LONG time.
You may want to also splurge a little and get your stuff from spectrapure. I went cheap one time and regretted it for a long time after.

Shirak · Jun 1, 2026

14ppm tds RO seems high. That's about 96% rejection if you are starting with 350ppm. I would look at that first and see what's going on there. Should be hitting 98% which would put your RO around 7ppm

@Buckeye Hydro can help you diagnose and troubleshoot what's going on with your rejection rate.

Kooma · Jun 1, 2026

Seems complicated.

I have 180tds tap water and run a 0.5 micron sediment filter, a 0.5 carbon block, the to membrane and then the di.

My donate before Di is usually 1-2tds, and 0 after Di. My Di lasts about 300-500 gallons, but maybe more. I don’t replace it very much, twice a year maybe?

14 after the ro seems off.