Ro Membrane Rejection

WVReefJunkie · Jan 5, 2021

Got a new add on canister for my four stage system. New Spectapure DI and SB filter, sediment and carbon also. Iam measuring after twenty four hours of run time 14 TDS out of my membrane. I found a calculator online which shows a 92.2 % rejection rate, should I change out the membrane?

Quietman · Jan 5, 2021

Depends on pressure too...operating under 65# (which I think is rated pressure) will impact Rejection Rate. 92 is a bit low, but 14 tds really isn't (mine is that when new). You may end up using a tad more resin so ...up to you. As long as your 0 TDS out the system you're good. Also they only last 3 years max I think so if it's older may be time.

Opus · Jan 5, 2021

WVReefJunkie said:
Got a new add on canister for my four stage system. New Spectapure DI and SB filter, sediment and carbon also. Iam measuring after twenty four hours of run time 14 TDS out of my membrane. I found a calculator online which shows a 92.2 % rejection rate, should I change out the membrane?

Yes, it is probably time to change it out. First I would remove it and reseat it just to make sure it isn't just an installation issue. You should be getting around 98% rejection, most say they guarantee around 95 to 96%. If you don't let chlorine get to it, a membrane should last 5+ years, of course that depends on how much water you are making and the tds of the water. My tap tds is over 400 and mine last 5+ years.

WVReefJunkie · Jan 5, 2021

I have 50 psi max readable on the gauge

WVReefJunkie · Jan 5, 2021

I use well water, and the tap tds is 180. I have noticed that it has been running for twenty four hours, and I have made about 35 gallons of product water. Iam going to measure the water to get a product to waste ratio. Maybe I should get a booster, to increase effectiveness?

WVReefJunkie · Jan 5, 2021

My product water to waste water 108/281. I have noticed that water pressure goes down from 50 psi to a minimum of 40 psi.

Randy Holmes-Farley · Jan 5, 2021

FWIW, I never got more than 95% rejection from my membranes. The value may depend substantially on what is present in the water.

WVReefJunkie · Jan 5, 2021

Randy Holmes-Farley said:
FWIW, I never got more than 95% rejection from my membranes. The value may depend substantially on what is present in the water.

I havent messed with water pressures much through my system, I was just thinking of ways to make my di filters last longer. I have a total of 400 gallons of water volume in my system.

JoshH · Jan 5, 2021

Randy Holmes-Farley said:
FWIW, I never got more than 95% rejection from my membranes. The value may depend substantially on what is present in the water.

Well FWIW I'm running dual Spectrapure 90 GPD membranes here and my incoming TDS fluctuates from 275-320ish and I get 0-1 TDS out of them. So it is possible given the right conditions.

Incoming water quality can definitely be a factor and as everyone's is different it can be hard to peg what a "Standard" system should be running at...

JoshH · Jan 5, 2021

WVReefJunkie said:
My product water to waste water 108/281. I have noticed that water pressure goes down from 50 psi to a minimum of 40 psi.

If your incoming PSI to the first membrane is 50 or below, this is FAR too low to be running dual membranes on. My incoming PSI runs between 85-90 and the pressure into the second membrane is 45. Which is barely usable from a good rejection rate standpoint.

Edit - Just realized you are running a single membrane, I would still look at giving your incoming PSI a boost. And possibly a new flow restrictor.

How old is this membrane?

WVReefJunkie · Jan 5, 2021

JoshH said:
If your incoming PSI to the first membrane is 50 or below, this is FAR too low to be running dual membranes on. My incoming PSI runs between 85-90 and the pressure into the second membrane is 45. Which is barely usable from a good rejection rate standpoint.

Edit - Just realized you are running a single membrane, I would still look at giving your incoming PSI a boost. And possibly a new flow restrictor.

How old is this membrane?

I would say 1 to two years, I cant remember for sure.

JoshH · Jan 5, 2021

Seems a rather short time for it to be performing at this rate. Has it always been this high? Or only after you swapped out the other filters?

WVReefJunkie · Jan 5, 2021

JoshH said:
Seems a rather short time for it to be performing at this rate. Has it always been this high? Or only after you swapped out the other filters?

I just purchased a canister filter from BRS with a TDS meter, so I never previous measured TDS after the membrane.

WVReefJunkie · Jan 5, 2021

I purchased the membrane Nov 24th 2018

JoshH · Jan 5, 2021

WVReefJunkie said:
I purchased the membrane Nov 24th 2018

What type of membrane is it? Size? Where did you purchase it from?

WVReefJunkie · Jan 5, 2021

JoshH said:
What type of membrane is it? Size? Where did you purchase it from?

WVReefJunkie · Jan 5, 2021

JoshH · Jan 5, 2021

Do you know what temperature your tap water is?

Sorry for all the questions, just trying to get a bead on your system overall

WVReefJunkie · Jan 5, 2021

JoshH said:
Do you know what temperature your tap water is?

Sorry for all the questions, just trying to get a bead on your system overall

I checked it at the waste water, 57.6 F

JoshH · Jan 5, 2021

Well your membrane is definitely performing well below it's spec rejection rate. Even with the low pressure and temp 92% is where most people would replace there membrane. Increasing the pressure might help a bit but I doubt you will see a significant change....