RODI reading help

[bh750]

Hi all,
I have a 5 stage RODI system. Just added new prefilters and even DI not too long ago. Have only made a couple hundred gallons or so. I have an inline TDS reader that reads at two points. First is after the prefilters and RO, before it goes to DI. Second is after the DI. Great setup but getting a strange reading...

1) First reading after 3 prefilters and RO membrane: .003 TDS

2) Second reading after going through DI: .014

???

Even though the DI is relatively new (maybe I've blown through it), I thought once the DI goes it doesnt do anything to the output, not better or worse.

Is it possible the DI is making the output higher in TDS?

 

[Randy Holmes-Farley Verified Community Expert]

Yes, the DI can output higher conductivity water if the things being released are more electrically conductive than the things coming in that may be displacing them from the DI resin.

That said, it is also possible one or both readings are in error.

Was the DI output 0 ppm TDS for a while?

 

[bh750]

Yes, the DI can output higher conductivity water if the things being released are more electrically conductive than the things coming in that may be displacing them from the DI resin.

That said, it is also possible one or both readings are in error.

Was the DI output 0 ppm TDS for a while?

Thanks Randy. Yep, the readings for years have been normal as espected. Typically my readings going into the DI would always be 2-4. Coming out would be 0 until the DI resin would degrade and it would climb and, I think, always match at worst the 1st reading. Have never seen it this high. And I replaced the resin not too long ago.

 

[Randy Holmes-Farley Verified Community Expert]

It could be the meter has an issue. Maybe remove and keep the DI resin (in case it is still good), and replace it with new, and see if the numbers drop.

 

[kenandmoose2]

With that low tds feed water to your resin beds that resin should last a very long time. I would suspect that meter is going out. We use cation and anion resin beds at work and regen them on a regular basis. It is basically the same di resin just split into a 2 step process We use sandfiltered river water to make demin water for boilers. The only time i have seen weird stuff happen with those resin beds was organic fouling from a floculant we were injecting in the sand filters. I dont imagine that could happen here. Not with single use resin. Old resin could be a problem but old is like 5 years old. Maybe your lfs has a hand held tds meter they could use to test it for you.

 

[bh750]

ok thanks all. let me see if its the meter first. will post result...

 

[GoVols]

ok thanks all. let me see if its the meter first. will post result...

Tagging along.

 

[bh750]

Update on this. Finally got a chance to make some new water. I think it turns out to be my TDS Meter. Not broken per se. My meter says the longer it runs the more accurate the reading. It stays on for 10 mins before going into batter save mode. Never had a problem before - the initial readings were usually the same as the later readings. Well now it seems I need to wait 5-10 mins for them to stabilize. At least that's what I'm thinking.

 

[GoVols]

Update on this. Finally got a chance to make some new water. I think it turns out to be my TDS Meter. Not broken per se. My meter says the longer it runs the more accurate the reading. It stays on for 10 mins before going into batter save mode. Never had a problem before - the initial readings were usually the same as the later readings. Well now it seems I need to wait 5-10 mins for them to stabilize. At least that's what I'm thinking.

So your saying if you let it run for awhile the meter reads zero?

 

[bh750]

Not exactly. After I let it run for awhile the TDS out from my RO membrane is higher or the same as the TDS coming out of my DI cartridge, as expected. When I first start the TDS meter the reading out of the RO membrane is 2-3PPM and the DI cartridge is 8-12PPM. Now they both read the same after a few mins. Also means myDI cartridge is done already!!

 

[GoVols]

Also means myDI cartridge is done already!!

+1

 

[kenandmoose2]

Do you use color change resin?

 

[bh750]

I do.

 

[Fishfinder]

I burn through DI resin every 60-70 gal. So if you made over 100 gal with 12ppm water id say it's used up

 

[kenandmoose2]

What pressure is your ro running at? The ro membranes work best around 85-100psi line pressure. I had to a add a small pump to mine to boost the pressure. Less waste water and cleaner ro water.

 

[Fishfinder]

It's at 60psi. My problem is that my TDS going in is around 980-1020.