RO/DI, Can't get TDS below 3ppm

[ThaChad]

Hey all,

I just rebuilt my entire RO system. It's a 3 Pre-stage (Sedament, Carbon Block, Carbon Block), 150 GPD Membrane (98% Rejection Rate, VERIFIED), Dual 10" DI filter. My tap water does run threw a Water Softener.

My Tap water is 286 TDS, after the membrane I'm at 5-6 TDS (98% Rejection Rate), I do have a booster pump and the PSI going into the membrane is 100psi. I am running a 1200ml flow restrictor (3/1 ratio)

I use to only have a single 10" DI filter, and was only able to get it down to 3ppm, so I JUST today, upgraded to a DUAL 10" DI filter (all new resin), to catch that last 3ppm of TDS, but instead, I'm getting the exact same 3ppm.

So effectively that 2nd DI filter isn't doing anything?

Any one have any ideas?

The membrane is rated for up to 130PSI, I could increase the booster pump to 110 or 120 PSI maybe? That may increase the rejection ratio? But that still doesn't explain why after the DI stage, I'm not getting any more rejection from 2 DI filters than 1..

Thanks!

-ThaChad

[tkeracer619]

Few questions...

What municipality are you purchasing water from? Always a good idea to look at the water quality report.

Why are you trying to push this much water? Contact time is everything in a RODI system. We have roughly the same capabilities and I have over 1000gal of water in the house. I'd suggest backing down to a spectrapure 99% rejection membrane or at least moving your 3:1 to 4:1. This will help with rejection.

You can boost pressure, that may help with rejection but will degrade contact time through the prefilters and DI.

What DI resin are you using? I assume it is fresh... Color changing or not?

Lastly, what TDS meter are you using? Can you verify that 3 is 3? Could be a case of a faulty TDS meter or one that needs calibration.

[jurgenph]

TDS meter not reading correct?

3 TDS out of a brand new di cartridge seems not right.

Try a different TDS meter?


J.

[ThaChad]

Few questions...

What municipality are you purchasing water from? Always a good idea to look at the water quality report. It’s a small town, 1,200 people, they have a well and a water tower. I live in a newer area with newer plumbing, but it’s on the far side of town from the water tower, so the water travels threw alot of old water lines.. They do send us an annual water report. I never really look at it.. I know the water has tannins in it..

Why are you trying to push this much water? Contact time is everything in a RODI system. We have roughly the same capabilities and I have over 1000gal of water in the house. I'd suggest backing down to a spectrapure 99% rejection membrane or at least moving your 3:1 to 4:1. This will help with rejection.

You can boost pressure, that may help with rejection but will degrade contact time through the prefilters and DI.

What DI resin are you using? I assume it is fresh... Color changing or not? I get my DI resin from Filter Direct, it says it is “Nuclear grade with color indicator: for production of demineralized water of high purity, silica free, When the resin is used up, the green color resin will change to brown color. It will give you 0 ppm TDS, Conductivity attainable less than 0.1uS/cm or resistivity of close to 18 meg.ohm

Lastly, what TDS meter are you using? Can you verify that 3 is 3? Could be a case of a faulty TDS meter or one that needs calibration. How do you verify? I’m not even sure it can be calibrated? It shows “0”, untill I stick it in the water. So, no I have no way to verify that 3 is 3.. Or if it’s accurate.. It’s an “IntelliTEC” brand TDS meter...

I am wondering if it won’t read lower than 3ppm and maybe it is “0”.. Is there one you guys can recommend? I can’t afford a super expensive one, but I’m sure there are good inexpensive ones out there..

Thanks,

-ThaChad

[Vinny Kreyling]

When I wanted to go with a 2-1 system I was told unless I had very soft water to forget it.
I would go with a 4-1 ratio as a first step.
You are pushing it, just because your car will do over 100 MPH there is no reason to do it.

[ThaChad]

When I wanted to go with a 2-1 system I was told unless I had very soft water to forget it.
I would go with a 4-1 ratio as a first step.
You are pushing it, just because your car will do over 100 MPH there is no reason to do it.


I have a 150 GPD membrane, I have a 1200ml flow restrictor.

I haven’t found a flow restrictor any larger...

Also, before my 1200ml flow restrictor came in, I was just using a valve and I was unable to achieve any lower TDS... my TDS after the Membrane is only 6ppm.

My water is 0 hard.

-ThaChad

[JMetaxas]

It must be your TDS meter.

[Opus123]

I'm in the same boat. I've got a 99% rejection spectrapure membrane and getting 4 tds out with 400 tds tap water. I've been getting a reading 2 out of my di cartridge so got a new package of DI. When I went to install it yesterday I noticed my DI was gold colored at the top half of the cartridge but normal color for the bottom half. Didn't think too much about it since I was changing it and emptied out the cartridge and put the new di in. I let the system run for about 15 minutes and tested my water after the di and it is still 2. Not sure what is going on. Can you pack the di too tightly? I have a second tds handheld put couldn't find it last night. Hoping I can find it tonight to verify the 2 tds. If they both read the same then I guess I'm going to take a little of the di out of the cartridge to see if that is the issue. Not sure if the di cartridge can become clogged or go bad.

[alton]

TDS meters do go bad and not that expensive to replace. DI resin is suppose to be packed tight

[HBtank]

The TDS meters commonly used make me wary when it comes to very low readings.

These meters do not seem particularly good at differentiated very low ranges from 0-3 ppm, yet this kind of resolution is what replacement is based on. In some ways I think the expectation is to trust that the filter is doing its job and that two stages of DI give redundancy, but like I said, I am wary.

I personally also have a handheld meter (COM100) to verify (and even those need to be calibrated periodically), but have ultimately decided on a three stage DI system as the only way to get the redundancy I want going forward. I am on the cautious side.

[ThaChad]

Well, I just checked my water in a clean clear glass, and the TDS meter shows "0". I then stick it in a bucket with the same water and it shows 10... So there must be residual salt or something that it's getting from the food grade bucket...

Anyway, If it shows "0" in a glass, than I'm confident atleast that the water is "0".

-ThaChad

[Opus123]

Well, I just checked my water in a clean clear glass, and the TDS meter shows "0". I then stick it in a bucket with the same water and it shows 10... So there must be residual salt or something that it's getting from the food grade bucket...

Anyway, If it shows "0" in a glass, than I'm confident atleast that the water is "0".

-ThaChad

Glad it worked out for you. I tested mine with 3 different tds meters tonight and they all read 2 coming out of the brand new DI. I'm wondering if something is wrong with the di cartridge.

[ThaChad]

Glad it worked out for you. I tested mine with 3 different tds meters tonight and they all read 2 coming out of the brand new DI. I'm wondering if something is wrong with the di cartridge.

Do you test yours in the container you fill? If so, try ising a clean glass and checking. From now on, that is how I will check mine.

-ThaChad

[Opus123]

Do you test yours in the container you cill? If so, try ising a clean glass and checking. From now on, that is how I will check mine.

-ThaChad

I tried the container and 2 different clean glasses and they all read 2 on 3 different tds meters. I'm wondering if I lost a rubber piece on the di cartridge. Is there supposed to be one on the top of the cartridge? There is one on the bottom.

After looking at some pics, I'm now wondering if I have it in upside down! Will it fit upside down? I need to check tonight.

[Gatorfan]

It sounds like you have it upside down. The gasket should seal it at the top, like the other cartriges.

[ThaChad]

I tried the container and 2 different clean glasses and they all read 2 on 3 different tds meters. I'm wondering if I lost a rubber piece on the di cartridge. Is there supposed to be one on the top of the cartridge? There is one on the bottom.

After looking at some pics, I'm now wondering if I have it in upside down! Will it fit upside down? I need to check tonight.

No, DI cartridges only have a seal on the top.. The threaded on cap that you fill the cartridge from, goes on the bottom.

-ThaChad

[Opus123]

Well, I feel like an idiot. Guess at some point I turned the cartridge upside down when refilling it and just thought that was the correct way going forward. Flipped it last night and now I'm getting 0 tds. Now I just need to dismantle the thing and put on all the new parts I've bought to upgrade it.

[Buckeye Hydro]

You're not the first... believe me!

Russ

[Buckeye Hydro]

Guys - there was an issue raised early in the thread about adding pressure to improve rejection. Although technically correct, you'll find that once you meet and exceed the factory test pressure (50 psi for Filmtec), adding pressure to improve rejection is a game of diminishing returns.

Russ