Time for a new RO Membrane?

TheEngineer · Feb 7, 2018

I can't recall the last time I swapped out my RO membrane (probably around 4 years ago). I've noticed my outgoing TDS has crept up from a typical 1-3ppm to 3-5ppm coming out of the RO stage. Is this my indication to change the membrane out?

KJAG · Feb 7, 2018

Few other variables needed. Your RO unit isn’t plumbed to your ATO right? What’s the TDS of your tap? What’s your rejection rate? Are you using quality cartridges/ when’s the last time you replaced them? Also if you’re relying on those inline TDS gauges they’re likely inaccurate.

TheEngineer · Feb 7, 2018

Input TDS: ~150 (varies, but I'm on a well)
Input pressure: 85 PSI
Rejection rate @ 5ppm: 96.6% @ 1ppm: 99.3%

I last replaced the pre-filters in 2016. I use an inline TDS meter, but verify with a handheld.

This is not hooked into an ATO.

Opus · Feb 7, 2018

You are still within specs for the normal membrane so you are probably good. It all comes down to costs at this point. The higher your tds the faster you will use up your DI. At tds of 2, you will get around 2200 gallons out of your di. At 5 tds you are only looking at 890 gallons from your di.

Actuarious · Feb 7, 2018

Opus said:
You are still within specs for the normal membrane so you are probably good. It all comes down to costs at this point. The higher your tds the faster you will use up your DI. At tds of 2, you will get around 2200 gallons out of your di. At 5 tds you are only looking at 890 gallons from your di.

Is this assuming no CO2? So if I have 7TDS going in and my cartrage lasts about 150-200 gallons, is the rest due to CO2?

TheEngineer · Feb 7, 2018

I have high CO2. I degas the water before going through DI

bif24701 · Feb 9, 2018

TheEngineer said:
I have high CO2. I degas the water before going through DI

That is a good move on your part.

I find that inline TDS sensors are more accurate than hand held simply because the water will quickly absorb anything it can from the air, container anywhere.

I would replace it. 96% at 85 PSI isn’t good performance. Be sure to check the carbons blocks, if they allow any chlorine/ chloramines through to the RO membrane they will oxidize it thus degrading the filters performance.