Can a bad RO membrane increase TDS?

[Aquavaj]

Lately the TDS on my dual membrane setup has been creeping up and chewing through Di resin. TDS at the tap is 60 but still 40 after both membranes. The filters were due to be replaced so I did that and cleaned everything. Testing the first membrane alone I get 37 on clean output and 157 on waste. On the second membrane I got 5 from the clean output. I didn't bother measuring the waste as I could see something is wrong with the first membrane.

I don't know how old the membrane is as I bought the system used but could a bad membrane be leaching TDS back out like in this case?

 

[P-Dub]

Not so much leaching as not removing, so, yes.

 

[Mical]

Since you bought it used, I'd replace both membranes and all filters so you have a "ground zero" starting point.

I have a dual membrane system and TDS IN = 208, after membranes = 4

 

[c.poindexter]

I agree, Replace everything and get a good start.

 

[Aquavaj]

Not so much leaching as not removing, so, yes.

But how could the TDS of the waste+clean be more than the source?

 

[P-Dub]

Its a PPM thing. The concentrations are greater as a function of volume. More volume at the source vs the waste.

 

[P-Dub]

But how could the TDS of the waste+clean be more than the source?

It's a PPM thing. The concentrations are greater as a function of volume. More volume at the source vs the waste.

 

[Aquavaj]

Since you bought it used, I'd replace both membranes and all filters so you have a "ground zero" starting point.

I have a dual membrane system and TDS IN = 208, after membranes = 4

The second membrane was only added about a year ago and hence the 4 TDS when I tested that membrane alone.

It's a PPM thing. The concentrations are greater as a function of volume. More volume at the source vs the waste.

Ah, got cha. That makes sense.

 

[Jackson2]

I had a water softener installed and was told to install the RODI system after the water softener. TDS in is 2 out 0. Membranes seem to last a while.

 

[Mical]

The second membrane was only added about a year ago and hence the 4 TDS when I tested that membrane alone.


Ah, got cha. That makes sense.

I think for peace of mind, I would replace all membranes and filters. It would keep record keeping of maintenance simpler than estimating how long one vs the other has been used for.

 

[Aquavaj]

So I bought a pretty cheap 100gpd membrane off of amazon and have it as the secondary. New sediment and carbon blocks. Added another filter housing for a Spectrapure Maxcap and then to a Spectrapure Standard DI. Upped psi to 80 and now getting 1 TDS out of the second membrane. Unless I have high CO2 that I'm not aware of this should greatly extend my DI resin life. At $25 a pop for the membrane replacing it every 6m-1yr won't be an issue. I'm happy now.