View Full Version : Super high TDS: crazy to put ro water through another membrane?

02/03/2015, 08:18 AM
I have a well and the TDS (post-water softener) is often >1000. I'm using your membrane (the 99% rejection one) and I'm getting very close to 99% off the membrane (usually 10-20 TDS).

I also have high CO2 so right now I collect the RO water in a brute trash can and sparge with an airstone. Then I put it through DI using a delivery pump.

My question is... What if I bought a second RO unit from you guys (one with an adjustable flow restrictor, so I could get 2:1 waste : product) and ran the RO water (after sparging, it would be in a brute trash can, which is ~10-20 TDS) through the second RO unit using a 6800 or 8800 aquatec pump? Then I'd have it go to DI post RO.

Is that a crazy idea? I figure that would give me <1 TDS water prior to DI and would save a ton of money on DI resin.

I'm not concerned about water usage (it's cheap to pull up the water and my waste goes into a pond in my yard), which I know would be an issue. But I can also mitigate the waste issue by getting a system with 2:1 or 1:1 waste.

Maybe I'm crazy, but I spend so much $$$ on DI resin that it just might be worth it (and I have regenerated it from time to time, but that's a huge pain)...


02/03/2015, 08:49 AM
What you propose is probably possible, but before you go to that extra expense and waste, I'd want to be sure you are really getting rid of as much CO2 as possible. You might like to get our CO2 Test Kit:


and be sure you are getting that CO2 down to around 5ppm (you'll never get rid of all of it by sparging). More air and more time may be needed. 10ppm by itself should not be killing your DI.

Support at SpectraPure

02/04/2015, 08:28 AM
Thanks. I have the CO2 kit. I have 140 ppm CO2 from the membrane (last time I checked) and I checked the aeration tub last night and it was ~10 ppm CO2.

If I just wanted to run the 10 ppm RO water through a membrane (no pre-filters), could I do that with just a membrane, housing, 8800 pump, and adjustable flow restrictor? I assume I could dial in 1:1 and not waste too much of the sparged RO water.

It wouldn't be that expensive because I have the pump already. I think I would just need a membrane with housing and the flow restrictor (and likely a flush valve), right?

Even if I still have CO2, I figure supplying 1 PPM TDS water (versus 10) will help save a lot of DI resin.

02/04/2015, 09:49 AM
co2 passes through the membrane. The best advice I can give you is add more airstones, a mag pump, and let it sit overnight. Then check the co2. Also if the air isn't removed from bottle B, then the test could be off. Also pre-filters are very important. Who knows what kind of organics reside in the well.