Do I need a new RO membrane?

hllb · Feb 10, 2020

My membrane is only about 5.5 months old. I asked my husband to start running water for me tonight and he accidentally put it on hot rather than cold. I got 5 gallons in 2 hours instead of 5 hrs. Not sure if it was all the way on hot but the bucket is over 105 degrees so probably...did that hose my RO membrane? It used up about 1/3 of my DI resin.

60CubeReefer · Feb 10, 2020

What was the output TDS before running with hot water vs after?

What is your current input/output TDS? If it goes beyond spec of your membrane, it's time to replace.

hllb · Feb 10, 2020

60CubeReefer said:
What was the output TDS before running with hot water vs after?

What is your current input/output TDS? If it goes beyond spec of your membrane, it's time to replace.

The water was still 0 TDS. It’s about 450 going in, at least when the water is cold. Would it differ for hot water?

60CubeReefer · Feb 10, 2020

I'm guessing it was 0 TDS after the resin. What was it before the resin (output of the membrane before it goes through the DI)?

hllb · Feb 10, 2020

60CubeReefer said:
What was the output TDS before running with hot water vs after?

What is your current input/output TDS? If it goes beyond spec of your membrane, it's time to replace.

Oh wait, do you mean the TDS prior to the DI? I have an RO buddy so no inline TDS meter.

FactoryKTMmotocross46 · Feb 10, 2020

Check the manufacturer's specifications or contact them. Dow has some info on how temp affects the performance of their membrane but no specific temps that I saw.
Dow filmtec

hllb · Feb 10, 2020

Ran some water and pulled a sample before DI. 450 in, 25 out. I didn’t test it this way before so can’t compare to before.

60CubeReefer · Feb 10, 2020

That's not great, 95% rejection rate. As an example, here in SoCal our TDS is in the 4-500 range as well, and my output is half of yours, ~12 TDS.

hllb · Feb 10, 2020

60CubeReefer said:
That's not great, 95% rejection rate. As an example, here in SoCal our TDS is in the 4-500 range as well, and my output is half of yours, ~12 TDS.

Maximum water temp: 105...fail LOL

Shawn.B · Feb 10, 2020

hllb said:
Ran some water and pulled a sample before DI. 450 in, 25 out. I didn’t test it this way before so can’t compare to before.

Your unit will produce water much faster at higher temperatures, this is why some (not many) people actually have mixing valves to supply their RO units with lukewarm water. As someone else dated I suggest you check the spec sheet on your specific membrane to see what temperature it can handle.
The rough way of checking your membrane will be taking a TDS reading after the membrane, I know you already did this and got 25, but take your reading after it runs for ~5min so you aren't measuring the TDS creep. So long as you are removing somewhere above 99ish Percent of your TDS you should be in decent shape.

hllb · Feb 10, 2020

Shawn.B said:
Your unit will produce water much faster at higher temperatures, this is why some (not many) people actually have mixing valves to supply their RO units with lukewarm water. As someone else dated I suggest you check the spec sheet on your specific membrane to see what temperature it can handle.
The rough way of checking your membrane will be taking a TDS reading after the membrane, I know you already did this and got 25, but take your reading after it runs for ~5min so you aren't measuring the TDS creep. So long as you are removing somewhere above 99ish Percent of your TDS you should be in decent shape.

I’ll check it again in a bit - running cold water through it now. If it’s toast, oh well. Might as well upgrade to the 100gpd.

Shawn.B · Feb 10, 2020

hllb said:
I’ll check it again in a bit - running cold water through it now. If it’s toast, oh well. Might as well upgrade to the 100gpd.

Plus you have someone else to blame!

hllb · Feb 10, 2020

Shawn.B said:
Plus you have someone else to blame!

It’s now 10 coming out of RO. So not optimal.

Shawn.B · Feb 10, 2020

hllb said:
It’s now 10 coming out of RO. So not optimal.

not horrible, but I would want to see that more in the 4-5 range. Useable though just keep in mind your DI will be used up faster

hllb · Feb 10, 2020

Shawn.B said:
not horrible, but I would want to see that more in the 4-5 range. Useable though just keep in mind your DI will be used up faster

My DI doesn’t last as it is. I have low water pressure. The first batch lasted maybe 8 weeks. Second batch 6 weeks. That’s at maybe 5g a week. Oy lol. I refill it myself with BRS resin now but I haven’t found a good way to pack it down well. I should probably just get a better system.

Flux Capacitor · Feb 10, 2020

Use a beer bottle to press the resin into the canister. It’s a win/win, the beer will help you forget about the cost to replace the resin every 6 weeks, and the bottle fits nicely in the opening