Burning Through DI Resin, how do I improve?

[MrTPlush]

I have a 4 stage BRS RODI unit and I think my city water is burning through the DI resin. I think I let the DI resin go to long and didn’t notice it was exhausted. Before replacing filters for every stage I noticed I have been getting 40 TDS out of it. Upon replacing (every stage ) and looking closely I see a huge portion is burnt through after one run of 25 gallons of water. That first run was 0 TDS, but now it is 1 TDS. I bought a TDS reader and the pre filter level is a very high 350ish at first reading out of the faucet.

How do I improve my water filtration and make it more economical? At this rate I won’t get much over 100 gallons without needing to replace DI resin. Are their sections I can add and plumb into my current 4 stage to help this? Thanks!

 

[Spare time]

Do you have a DI bypass valve when flushing the membrane?

 

[Midrats]

I'd guess you have high co2 in your water. That's my problem. You have to off gas it before the DI with an air stone .

 

[Opus]

First you need a copy of your most current water report from the city. Usually they have these on the website. This may help provide some insight. Also, you provided your tap water tds but not the tds after the ro membrane but before the di filter. This will also give us some insight on what might be causing your problem. My tap water can be up to 450 tds depending on the water level in the source lake and I have a tds of usually around 4 or 5 after my ro membrane.

 

[Midrats]

I have considered setting up a separate reservoir to off gas the RO, and then pumping it through the DI after 24 hours of vigorous aeration, but don't really have the room, nor do I want to. I mostly just leave the DI canister blank. The only thing that makes it past the membrane is silicates, and I'm not worried about silicates. CO2 chewing through DI resin is a well known issue.

 

[Uncle99]

Check your TDS just out of the membrane, if it’s more than 5 or 10 TDS, your membrane requires replacement.

DI is just a polisher and will exhaust quickly if the membrane is not taking out 95-99% of the source water TDS.

 

[MrTPlush]

First you need a copy of your most current water report from the city. Usually they have these on the website. This may help provide some insight. Also, you provided your tap water tds but not the tds after the ro membrane but before the di filter. This will also give us some insight on what might be causing your problem. My tap water can be up to 450 tds depending on the water level in the source lake and I have a tds of usually around 4 or 5 after my ro membrane.

Here is the most recent quality report.

I will work on getting the reading for TDS pre resin.

https://www.townofribmountain.org/vertical/sites/%7BE48D29A7-BE80-430E-97D5-C8EDB1E675F5%7D/uploads/CCR2020.pdf

 

[Midrats]

Put some of your fresh RODI into a container and check the pH. Aerate it for a while and check it again. If the pH is higher you'll know what your problem is.

 

[MrTPlush]

Put some of your fresh RODI into a container and check the pH. Aerate it for a while and check it again. If the pH is higher you'll know what your problem is.

I will make sure to do this when my Hanna PH checker arrives from BRS. I won’t bother doing this with the API tester I have now.

 

[Opus]

Here is the most recent quality report.

I will work on getting the reading for TDS pre resin.

https://www.townofribmountain.org/vertical/sites/%7BE48D29A7-BE80-430E-97D5-C8EDB1E675F5%7D/uploads/CCR2020.pdf

The report says they get their water from wells so CO2 could be your problem.

 

[MrTPlush]

First you need a copy of your most current water report from the city. Usually they have these on the website. This may help provide some insight. Also, you provided your tap water tds but not the tds after the ro membrane but before the di filter. This will also give us some insight on what might be causing your problem. My tap water can be up to 450 tds depending on the water level in the source lake and I have a tds of usually around 4 or 5 after my ro membrane.

I pulled the tubing prior to the DI and am running 35 TDS at that point.

 

[Cell]

For comparison, I'm down to 4 TDS pre-DI on my city water.

 

[Midrats]

I'm at 2 pre-DI city h20

 

[MrTPlush]

I'm at 2 pre-DI city h20

Sigh....I would be okay with like 5x that at this point.

 

[ingchr1]

A couple of things:

You may be getting creep giving high TDS out of the RO membrane when you first start making water. When I start making water I will let the RO go to the drain until the TDS on the RO out drops to less than 30. I have an RO storage tank with faucet, so I close the tank valve and open the faucet to do this. After getting the TDS down I will start making DI. On mine I have seen TDS on the RO out start in the couple of hundred range. It will get down to around 10 or so. My TDS in (well water) is in the 500 range. Also, when I'm not making water I shut off the water supply into the unit to minimize the TDS creep.

What helped me the most though was going from mixed resin to separate anion and cation chambers. The anion is lasting me a whole lot longer than the mixed did. The cation I haven't even seen change color yet. I've changed the anion once maybe twice in that time (don't recall as it's been over a years time span). I still have a mixed bed as the last stage. Which has changed color a little as I let the anion chamber go a bit too long before changing it.

 

[Opus]

I pulled the tubing prior to the DI and am running 35 TDS at that point.

As stated, if you didn't let it run for a few minutes first, then you are probably reading tds creep. You should take the reading after letting it run for a few minutes. With your 350tds tap water you should be getting a pre-di reading of between 4 and 11, which is between a 97 and 99% rejection rate. If it is over 18 then something is definitely wrong with the RO membrane because that would be less than 95% rejection and most are rated for 95 and above. If your pre-di is really 35 then a di canister will produce around 127 gallons of 0 tds water. Compare that to say 11 tds which will get you around 400 gallons of 0 tds from a di cartridge.

 

[MrTPlush]

As stated, if you didn't let it run for a few minutes first, then you are probably reading tds creep. You should take the reading after letting it run for a few minutes. With your 350tds tap water you should be getting a pre-di reading of between 4 and 11, which is between a 97 and 99% rejection rate. If it is over 18 then something is definitely wrong with the RO membrane because that would be less than 95% rejection and most are rated for 95 and above. If your pre-di is really 35 then a di canister will produce around 127 gallons of 0 tds water. Compare that to say 11 tds which will get you around 400 gallons of 0 tds from a di cartridge.

I let it run for five minutes:

Out of faucet - 640
Pre-DI - 33

Before I was reading the water coming right out of the faucet by just putting the probe in the running water....but letting some drain into a cup and then getting the reading gives the higher (and accurate) reading. That is about 95% rejection...so my unit is working, I am just getting murdered by stupid high TDS in my water.

 

[Water Dog]

How recently did you replace your prefilters and RO membrane? What brand RO membrane are you using? A Dow Filmtec should have a 98 to 99% rejection ratio. Spectrapure Spectra Select Plus membranes are batch tested rebranded Dow membranes that claim a 99% rejection ratio. What size micron prefilters are you using?

If you are using a Dow Filmtec membrane, a 95% rejection seems very low, hence why I asked what micron size prefilters you are using. With your membrane having to process such high TDS water, it’s important to make sure it is well protected to operate as efficiently as possible. So you should run with at least a minimum of 1 micron prefilters.

At a 98 to 99% rejection ratio, you should be getting between 6 to 13 TDS after your RO membrane with 640 TDS source water.

Are you using a DI bypass valve (not to be confused with a membrane flush valve) upon your system’s start up? Using one will do wonders for preserving your DI resin life. See my short write up below for an explanation of what a DI bypass valve is…

RO/DI - Are all equal?

Quite frankly, the only thing you need is the vertical DI kit. You already have everything else. Based on your numbers though, I do think you need a new RO membrane.

www.reef2reef.com

You should invest in a triple inline TDS meter with a sensor placed right before the last carbon block but before the RO membrane, one after the RO membrane and one after your DI stage. That way you can always monitor the efficiency of your system and maintain it as necessary.

 

[MrTPlush]

How recently did you replace your prefilters and RO membrane? What brand RO membrane are you using? A Dow Filmtec should have a 98 to 99% rejection ratio. Spectrapure Spectra Select Plus membranes are batch tested rebranded Dow membranes that claim a 99% rejection ratio. What size micron prefilters are you using?

If you are using a Dow Filmtec membrane, a 95% rejection seems very low, hence why I asked what micron size prefilters you are using. With your membrane having to process such high TDS water, it’s important to make sure it is well protected to operate as efficiently as possible. So you should run with at least a minimum of 1 micron prefilters.

At a 98 to 99% rejection ratio, you should be getting between 6 to 13 TDS after your RO membrane with 640 TDS source water.

Are you using a DI bypass valve (not to be confused with a membrane flush valve) upon your system’s start up? Using one will do wonders for preserving your DI resin life. See my short write up below for an explanation of what a DI bypass valve is…

RO/DI - Are all equal?

Quite frankly, the only thing you need is the vertical DI kit. You already have everything else. Based on your numbers though, I do think you need a new RO membrane.

www.reef2reef.com

You should invest in a triple inline TDS meter with a sensor placed right before the last carbon block but before the RO membrane, one after the RO membrane and one after your DI stage. That way you can always monitor the efficiency of your system and maintain it as necessary.

I replaced all the filters when I replaced the DI resin...so like a week ago and maybe 75 gallon of water ago. I have never replaced the RO membrane, but I have only had the unit running for like 4 months. It is all standard BRS stuff...so Dow RO, Puratex 5 micron sediment, BRS 5 Micron VOC, and BRS DI resin.

I don't have a bypass valve, but the last few times I have now started pulling the tubing pre DI to let it run for a bit....which I presume is just doing the same thing without having an adapter to run another line to dispose of water. I just let it drain into a bucket and then dump that out.

 

[Water Dog]

A 95% rejection rate for a 4 week old Dow Filmtec membrane is quite poor. A new membrane should have at least a 98% rejection rate. When you initially set up your system and later replaced the prefilters, did you flush the prefilters separately , sediment first followed by the carbon block without the membrane and DI in place? Without flushing your prefilters first, I’m wondering if the membrane got fouled if left in place downstream during the initial prefilter flushing process.