RO membrane question

Hamsternuts

Hamsternuts

New member
Howdy :wave:



I recently bought a deluxe 75 GPD RO/DI system from BRS. Everything was already hooked together except the DI system, which was very simple.

My question is, why can't I get close to 1 or 2 ppm coming out of the membrane, before the DI stage? I have 2 inline TDS meters, one of post RO and the other is post DI. I was averaging about 10 TDS post RO before I bought a boost pump. My line pressure (city water) was about 40-45psi or so. Now with the boost pump it's closer to 90psi and I still average about 6-8 TDS. I just want to lower the TDS coming out of the RO so I don't have to replace the DI resin so much. I've probably only made about 6-800 gallons of product water, and I've already burned through about 3 DI refills. I can't figure out what I'm doing wrong.

I do have a backwash valve for the membrane and do use it one a week or so. I don't have the TDS number for my tap water right now. I'm at work and would have to figure it out at home after plumbing tap water through an inline meter. I'll get it when I can.

Thanks.
 
Yes, and it is possible that you are already getting better than 98% rejection from the membrane, won't know how well it is performing until we know incoming TDS.
 
I am in Vegas and the water in the Southwest is generally very hard. I have measured as high as 700 ppm here. So getting 98% rejection would still leave 14 ppm. I have a 5 year old Dowtec 75 gpd membrane that is still getting 99%+ rejection. I check quarterly with a Com-1 meter. I never get 1-2 out of the RO though with the source water here.

Drew
 
Wow. 700TDS out of the faucet? I never really stopped to think about the percentages, and how that translates into post RO TDS. I just moved to AZ and haven't really thought much about the water here. I guess the house has a softener for a reason.
 
Just remember the softener does not lower TDS. It only exchnages ions. Generally sodium for calcium and such. That 700 is with a water softener also.

Drew
 
6-8 tds out of the membrane is very good and quite typical.

200 gallons per lb of di resin os typical as well. Get BRS refillable di cartidges to save money.
 
Ok,

I finally plumbed a tap water line through my inline TDS meter, and my tap TDS hovers around 390 +/- 25ppm. I guess with a 98% rejection rate my 6 or 7 TDS out of the RO is spot on.

I do have the refillable DI resin canisters. They're pretty easy to refill. I have come to really appreciate BRS and their stuff. I just hooked up a dual BRS reactor wth an MJ 1200 pump. It has both canisters full of carbon now, but works great.

I guess unless they invent a 99.99% rejection RO membrane, I'll be restocking DI resin from time to time.

Thanks for the input.
 
When you are ready to change membranes, you can get better ones, and they are not expensive. At the house in San Antonio, my incoming TDS hovers around 300 and post membrane is 1-2. Our new house at the lake has an incoming of 220 and a post membrane of a solid 1. The Spectrapure 98% minimum membrane is what makes the difference.
http://www.spectrapure.com/St_replac_p3.htm
Same high quality membrane that most better places sell, except they test them, the ones that meet the minimum 98% rejection are sold separately from the ones that don't. They are in Tempe, where the water is also very high in TDS, I know there used to be a member here who lived there and had 1100 TDS to deal with. When your water isn't so good, it pays in the long run to get the best membrane you can.
 
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