High TDS after RO membrane

Doc’sReef · Sep 3, 2024

Hello,
I have been having an issue with very high TDS levels after my RO membrane. I have changed my sediment filter and I have 3 carbon filters which are all new as is my 100gpd Dow membrane. My tap TDS here in Texas is around 350 and post membrane it’s still around 100! It’s eating up my resin very fast obviously and is not ideal. I have added an aquatic life booster pump as well to see if it would improve my efficiency.
I have ordered a second membrane and an additional carbon stage to try and see if it’s can get the levels down a bit more. The hope is passing the water through a second membrane will yield a better result. I have also ordered a pressure gauge.
I’m just at a loss as I never had this issue before in other states I’ve lived in and always was able to achieve a significant reduction in TDS after my membrane. Is there something vastly different with my source water that is not adequately being filtered out? It is municipal not well water.
Post resin the values are coming out at 0 but it’s exhausting the resin very fast.
I’ve allowed it to run for a bit to break in the new filters as well.
Any thoughts or ideas would be greatly appreciated.

Uncle99 · Sep 3, 2024

The membrane is expected to remove 95-99% of incoming, so 350 to 100 would indicate the membrane is not working correctly.

Why, well, that could be a few things.
Poor pressure, incorrectly installed membrane, a blown membrane are some we run into most often.

You should have no issue getting down to say 30-35ppm with one membrane.

Doc’sReef · Sep 4, 2024

Thanks for your reply.
In the past I’ve always seen a significant reduction in TDS after the water passed through my filters and membrane. So I completely agree with you on the expected reduction of TDS. I’m not sure as to why I’m getting these numbers.
I checked the seating of my membrane in the housing twice and it’s snug. My membrane is a brand new DOW filmtec 100 GPD from BRS.
I ordered another new membrane and will test it and see if there is anything changes. But beyond that I’m stumped and a bit surprised as reviewed all my plumbing.
Being that the source water is around 350 and post membrane is around 100 some filtration is happening but I’m assuming something at the membrane level is the cause of my problem.
I know it’s far fetched but could there is something in the source water that bad that it’s not removed from the membrane?

edd59 · Sep 4, 2024

could be a bad restricter valve or valve isnt matched to your membrane

Buckeye Hydro · Sep 6, 2024

edd59 said:
could be a bad restricter valve or valve isnt matched to your membrane

flow restrictors... are not valves.
But this brings up a good point. Line up 8 identical cups (solo cups work great). With your waste water tube in one hand and you purified water tube in the other, how many cups do you fill with waste in the time it takes to fill 1 cup with purified? This exercise will give you your concentrate to permeate ratio.

I suspect you may have a internal crack in your RO membrane housing. Measuring that ratio will help determine if this is the case.

Russ

Doc’sReef · Sep 7, 2024

Update,
So after a rather arduous experience of trial and error I was able to get a normal TDS reading after the membrane. I did a test and took one of my membranes and connected it directly to a spigot outside and my TDS came down to 14 from just north of 300 at the source.
Initially I had my RO system installed in my laundry room and took a Y connection off the cold water line that feeds my washing machine. When I did this the TDS post membrane was over 100. Mind you this was with the washing machine off just to avoid any variables. I did this before years ago when I was living in a condo and it worked perfectly. I can't account for why the difference in performance this time around but just thought I would share my experience.

Buckeye Hydro · Sep 7, 2024

Doc’sReef said:
Update,
So after a rather arduous experience of trial and error I was able to get a normal TDS reading after the membrane. I did a test and took one of my membranes and connected it directly to a spigot outside and my TDS came down to 14 from just north of 300 at the source.
Initially I had my RO system installed in my laundry room and took a Y connection off the cold water line that feeds my washing machine. When I did this the TDS post membrane was over 100. Mind you this was with the washing machine off just to avoid any variables. I did this before years ago when I was living in a condo and it worked perfectly. I can't account for why the difference in performance this time around but just thought I would share my experience.

I'd say you have a clue, but not a solution quite yet

Marcus H. · Sep 7, 2024

I run a booster pump on my system. I have well water high in HCo3 (mid 400s ppm). I can go TDS 640 to mid 40s. The booster pump improves efficiency of the system. Are you on well or city water? If it is well then it is most likely a pressure issue. (my pressure tank cycles 45 to 65). If you are running your washer then I could see you definately having low line pressure because of the Y connection.