Replaced RO membrane, and still get higher TDS?

[Phyber]

I have a BRS 4 stage RODI, and I recently ordered replacement filters for it as my others hadn't ever been swapped out. I got a new 1 micron sediment, 1 micron carbon, a DI mixed bed refill, and a DOW 75 gpd membrane.

I have well water that comes in at 60 TDS at the tap for my RODI, and I run an AquaTech booster pump from 75-80 psi, connected after the prefilters and before the RO membrane.

I installed the new filters, sans DI resin cartridge, and let it run off about 5 gallons of water, or an hour run time. I saw the TDS of the RO output hover around 1-2 TDS.

That was the last I ever saw of that. The next weekend I put my DI resin in and began making product water, and my RO output will not go below 4 TDS. Tried flushing in different intervals, won't budge.

Any idea what's going on? My original RO was putting out 5 TDS which is why I replaced it!

 

[adrianr514]

If possible I would bump your pressure to 90psi. Also, what is your rejection rate at?

 

[Phyber]

If possible I would bump your pressure to 90psi. Also, what is your rejection rate at?

I'll try upping this evening, and take a measure of waste : product. I want to think it's around 2 or 3:1

 

[Quietman]

That pressure should be fine really, but more can't hurt to improve a bit. Above 75-80# you're running is probably nominal improvements at best. You're running about 93% rejection so a tad low. You didn't say how old the previous membrane was used or if performance recently fell off, but if was in service less than 2 years then it might have been fine and the issue existed before.

So what's causing rejection rate to be low?

I think the run in time for measuring is 24-48 hours. I don't anyone that just runs their RODI just to run in the membrane though.

Is your water coming in unusually cold? Those ratings are based on 77 degrees plus/minus. Low temps cause low rejection.

Well water often has higher CO2 levels which aren't removed by RO membranes and can cause higher resin consumption. What's your pH on the well water? Lower could mean CO2 present.

 

[Phyber]

That pressure should be fine really, but more can't hurt to improve a bit. Above 75-80# you're running is probably nominal improvements at best. You're running about 93% rejection so a tad low. You didn't say how old the previous membrane was used or if performance recently fell off, but if was in service less than 2 years then it might have been fine and the issue existed before.

So what's causing rejection rate to be low?

I think the run in time for measuring is 24-48 hours. I don't anyone that just runs their RODI just to run in the membrane though.

Is your water coming in unusually cold? Those ratings are based on 77 degrees plus/minus. Low temps cause low rejection.

Well water often has higher CO2 levels which aren't removed by RO membranes and can cause higher resin consumption. What's your pH on the well water? Lower could mean CO2 present.

The old RO membrane was the original one in the RODI unit I purchased back in 2010. I got out of the hobby for about 5 years, and when I fired the unit up again it was putting out 5 TDS, which I used for a little while. Then I got this new membrane...

Incoming cold water is indeed cold. I don't have a temp on it but I'm sure it's not 77.

I know I have CO2 in the water, my DI resin is only putting out about 50 gallons of 0 TDS water before being exhausted. That's why I'm looking to fix my RO to as little output as possible to help with lifespan.

 

[Quietman]

The old RO membrane was the original one in the RODI unit I purchased back in 2010. I got out of the hobby for about 5 years, and when I fired the unit up again it was putting out 5 TDS, which I used for a little while. Then I got this new membrane...

Incoming cold water is indeed cold. I don't have a temp on it but I'm sure it's not 77.

I know I have CO2 in the water, my DI resin is only putting out about 50 gallons of 0 TDS water before being exhausted. That's why I'm looking to fix my RO to as little output as possible to help with lifespan.

Ah...I'm not aware of anything but degassing and/or resin to reduce CO2. I shifted to the three stage DI resin (Cation/Anion/Mixed) to reduce consumption. I don't have CO2 but was burning through mixed only like crazy with other impurities. But I believe with CO2 you're still going to go through mixed (Anion needs to be first for CO2) but it should be at a reduced rate than before.

Degassing sounds like a pain to me, but with a booster pump and air stone it could be pretty cost effective if you have room and desire.

 

[Phyber]

Ah...I'm not aware of anything but degassing and/or resin to reduce CO2. I shifted to the three stage DI resin (Cation/Anion/Mixed) to reduce consumption. I don't have CO2 but was burning through mixed only like crazy with other impurities. But I believe with CO2 you're still going to go through mixed (Anion needs to be first for CO2) but it should be at a reduced rate than before.

Degassing sounds like a pain to me, but with a booster pump and air stone it could be pretty cost effective if you have room and desire.

Right, I understand about DI and CO2...

I'm trying to find info on how to tell a defective RO membrane. I've gone through three BRS reps and they keep telling me to run it for 24 hours and use it for years.

If 4 TDS really is the best I'll get, then what was I seeing for an hour when it was 1-2 TDS constantly? Why won't I ever go back down to that level despite using a booster pump and flushing before and after a run?

 

[Quietman]

Right, I understand about DI and CO2...

I'm trying to find info on how to tell a defective RO membrane. I've gone through three BRS reps and they keep telling me to run it for 24 hours and use it for years.

If 4 TDS really is the best I'll get, then what was I seeing for an hour when it was 1-2 TDS constantly? Why won't I ever go back down to that level despite using a booster pump and flushing before and after a run?

Understanding I'm not a product expert on RO membranes (but BRS team is as close to one as we're going to get as hobbyists), I would say yes, 4 is probably as good as it'll get if it's CO2 and your orings, seals and system are all functioning correctly. It also matched your previous membrane.

Not sure why the initial was 1-2 ppm, but I do know run in times are stated for a reason and initial readings are not valid long term. Meaning they are neither best or worst and until run in complete, not something I would use for comparison.

 

[Uncle99]

Your DI resin is packed very tight right and there are no leaks, even tiny right?
The water is following up through the canister not down right as this mitigates channeling.
Are these statements correct?

 

[Phyber]

Your DI resin is packed very tight right and there are no leaks, even tiny right?
The water is following up through the canister not down right as this mitigates channeling.
Are these statements correct?

Yes, packed with a tool and even DI consumption.

DI is not my concern though! My RO output, considering it's at 60 TDS in, is 4 TDS out. What might have caused it to not stay around 1-2 TDS?

 

[Opus]

Are you using a handheld tds meter or inline? Inline meters do not compensate for temperature but the handheld does. Not sure how much of a difference that makes.

I would really expect you to be at 1 tds. My incoming tds is 400+ and my tds before my di is 4 to 5.

 

[Phyber]

Are you using a handheld tds meter or inline? Inline meters do not compensate for temperature but the handheld does. Not sure how much of a difference that makes.

I would really expect you to be at 1 tds. My incoming tds is 400+ and my tds before my di is 4 to 5.

Inline TDS. I also would expect to be lower

 

[Shirak]

I am on well water also and it is cold.... reduces the output quite a bit but rather not deal with warming it first! What are the specs on the membrane? many are 96% rejection under the best of circumstances. Some will go to 98%. I also found it takes a little while to get there.. My water is hard with around 250 tds eventually my 98% hi flow AMI membrane will get down to 4 tds fairly quickly and eventually will hit 2 tds after 10 minutes or so. Which is better than it should be but I run with no restrictor in the waste line so that may help. I have also noticed where I am the well water tds can vary quite a bit depending on season and recent rainfall. Wells are pretty shallow up where I am.

edit: I just looked up the specs on my AMI membrane and it has 99.5% stabilized rejection (not 98%)

 

[Phyber]

I am on well water also and it is cold.... reduces the output quite a bit but rather not deal with warming it first! What are the specs on the membrane? many are 96% rejection under the best of circumstances. Some will go to 98%. I also found it takes a little while to get there.. My water is hard with around 250 tds eventually my 98% hi flow AMI membrane will get down to 4 tds fairly quickly and eventually will hit 2 tds after 10 minutes or so. Which is better than it should be but I run with no restrictor in the waste line so that may help. I have also noticed where I am the well water tds can vary quite a bit depending on season and recent rainfall. Wells are pretty shallow up where I am.

edit: I just looked up the specs on my AMI membrane and it has 99.5% stabilized rejection (not 98%)

so far, with this booster pump, output volume isn't bad compared to when I was just on tap pressure (~40psi). I want to keep this up, but cleaner...

I have a DOW FIlmtec 75 gpd membrane, 96%-99% stabilized rejection rate at ideal conditions. My 60 incoming tds starts after the RO at ~15 tds then drops quick to ~8, then slowly ramps down and stops at 4. It'll hold at 4 for as long as I'm making water.

 

[Scrubber_steve]

Inline TDS. I also would expect to be lower

I would buy or borrow a pen type meter & see what readings you get from just the RO outlet, & then after the DI outlet.

 

[Shirak]

There is always an initial flush after it sits for a bit. Mine is around 100 tds initially when I first open the valves and it takes a minute to drop down to 4-5 at which point I open the DI line. 96% of 60 would probably read around 3 on the meter so may not be that way off base?

 

[destro]

I'm in a similar situation as you so following to see if I can learn something.

I've had my RODI unit for a very long time and always trusted my inline TDS which always showed zero.
I had a 'if it's not broken why fixed it' mentality. My ignorance caught up to me. This summer a friend came over and saw my RODI and was shocked how light in colour the DI resin was. I told him I never changed it or the membrane because my TDS meter showed 0. I've only ever changed the carbon and the pre-filter. You probably know how that conversation went from there.

After replacing all the stages (like new), it was the first time I ever saw the TDS meter read anything other than zero; except for the count down when you first plug the unit in. The first 5 minutes of running the RODI, always starts around 50-60 and then gradually down to 4-5. After about 10 minutes it reaches 2. At about 15 minutes it flickers between 1-2.

So here I am... wondering if my RODI is working correctly.
Was my TDS so high that it gave me a 0 previously?
Why is it still giving me 1-2 when all my stages have been replaced? Is this normal?
Is my line TDS meter not working? Should I invest in a hand held TDS meter?

 

[GainesvilleReef]

Just like bubbles can affect salinity probes, trapped air can affect the TDS sensors in a RODI system. Same principle. A new dry TDS system will always have some trapped air at first. And that could explain initial low readings. My opinion is that your RO output is reasonable.

 

[Pntbll687]

I have a BRS 4 stage RODI, and I recently ordered replacement filters for it as my others hadn't ever been swapped out. I got a new 1 micron sediment, 1 micron carbon, a DI mixed bed refill, and a DOW 75 gpd membrane.

I have well water that comes in at 60 TDS at the tap for my RODI, and I run an AquaTech booster pump from 75-80 psi, connected after the prefilters and before the RO membrane.

I installed the new filters, sans DI resin cartridge, and let it run off about 5 gallons of water, or an hour run time. I saw the TDS of the RO output hover around 1-2 TDS.

That was the last I ever saw of that. The next weekend I put my DI resin in and began making product water, and my RO output will not go below 4 TDS. Tried flushing in different intervals, won't budge.

Any idea what's going on? My original RO was putting out 5 TDS which is why I replaced it!

Sorry if I missed it in the thread but do you know the TDS of the tap water going into the prefilters?

As for the C02, look into a 3 stage DI resin with separate cation, anion and mixed bed cartridges. It took me from getting 100-125g of water on a single mixed bed to getting about 300g of water and just replacing the anion resin. I've made over 1000g of product water and have yet need to replace the mixed bed or cation resins, the anion has been changed about 3 times.

 

[Shirak]

I'm in a similar situation as you so following to see if I can learn something.

I've had my RODI unit for a very long time and always trusted my inline TDS which always showed zero.
I had a 'if it's not broken why fixed it' mentality. My ignorance caught up to me. This summer a friend came over and saw my RODI and was shocked how light in colour the DI resin was. I told him I never changed it or the membrane because my TDS meter showed 0. I've only ever changed the carbon and the pre-filter. You probably know how that conversation went from there.

After replacing all the stages (like new), it was the first time I ever saw the TDS meter read anything other than zero; except for the count down when you first plug the unit in. The first 5 minutes of running the RODI, always starts around 50-60 and then gradually down to 4-5. After about 10 minutes it reaches 2. At about 15 minutes it flickers between 1-2.

So here I am... wondering if my RODI is working correctly.
Was my TDS so high that it gave me a 0 previously?
Why is it still giving me 1-2 when all my stages have been replaced? Is this normal?
Is my line TDS meter not working? Should I invest in a hand held TDS meter?

If everything is running properly you should be reading roughly 2-4 tds after the RO unit going into the DI cartridge. After DI you should be reading 0. I put a diverter valve after the RO membrane before the DI cartridges so I can let the RO run for a few minutes since it will be high in tds initially (perfectly normal). Then I can switch the flow to go through the DI and collect RODI water for mixing. I use the RO water for my coffee machine and watering plants. Makes great coffee! After the BRS video on various DI cartridges I am also using the 3 cartridge setup with pure anion first then cation and a mixed bed last.

I also agree with the others in that it is helpful to know what your tds is from your water source as this will affect your RO tds reading since it's a % removal basis. And equally important is which carbon block you use if on water treated with chlorine or chloramine. If they get through to the membrane they will punch holes in it and make it less effective at removing all the other things you are trying to filter.