0 to 1 TDS after only a few uses?

chris_pull · May 29, 2021

I’ve been using a 5 stage RO/DI system with a dual membrane installed in series. Both membranes are 50 gpd. I’ve used the system about 6 times over the course of a couple of months, making about 10 gallons or so each time. TDS before RO is about 260, and after both membranes, and before DI, 7 TDS. Up until now I’ve had 0 TDS from my product lien but today I noticed I’m getting a 1TDS reading.

I thought perhaps the dual membranes were burning the resin faster but 7 TDS before DI doesn’t seem too bad from what I’ve read online.

Any thoughts on what’s going on? I’m new to RO/DI so hope I've not made a any mistakes!

I have an inline HM TDS meter and the flow restrictor is 450. This is the flow restrictor that came with the system but when I ordered the second membrane it came with a lower restrictor (I think 300) and I was unsure which to use.

wmchaseb · May 29, 2021

I was having issues burning through di resin and I added a t valve after the ro portion. When you first turn on the unit you have tds creep and it can cause you to burn through di resin. When I first start my rodi unit I turn the valve to run the RO product water down the drain. After about 5-10mins or once my ro water tds has stabilized (around 5tds for me) I turn the valve to allow the water to go through the di resin. Since then my di resin last at least 4x as long if not longer.

lapin · May 29, 2021

7 after 260 is about right for a 95% membrane. So its not the RO part.
It could be whats in the 7 thats causing fast resin depletion. Co2 from well water. Salt from a water softener ect....
You could try the above method to see if that makes a difference.
I could also be the TDS meter. 0 and 1 are pretty close.

Screwgunner · May 29, 2021

Do you mix in the same container. Resido salt will cause tds

SteveMM62Reef · Jul 12, 2021

My Seven Stage, 150 GPD started doing the same thing. I had the water tested by someone I know, with a meter that is more sophisticated. He does water systems maintenance. Came up Zero on every sample. He said my sensor(s) needed cleaning, but he had no idea on how to clean them.