Chromium in RODI?

ChadmRoman · Feb 12, 2020

Chasing high chromium for the last three ICP Triton Tests. Just purchased and received a hanna chromium LR checker to test all water sources. Found the RODI water using aquatic life 4 stage shows steady readings at 12 ppb. Tested a freshly mixed salt and read 12 ppb. Tested the RODI with a TDS and reads 0. The cartridges were changed out around Christmas.

Is it possible the RODI unit isn't removing chromium? Should I add additional cartridges for carbon?

Latest ICP Test

Element	Analysis	Setpoint	Deviation
Cr	17 µg/l	0,1 µg/l	16.90

purp · Feb 12, 2020

There isnt a relationship between TDS and chromium. Have you checked your source water TDS prior to RODI?

Opus · Feb 12, 2020

The RO membrane should remove 96-98% of the chromium.

ChadmRoman · Feb 13, 2020

purp said:
There isnt a relationship between TDS and chromium. Have you checked your source water TDS prior to RODI?

Source water tds is 45
It’s city water supply and brs said I should use a five stage not four which basically adds another carbon block

ChadmRoman · Feb 13, 2020

Opus said:
The RO membrane should remove 96-98% of the chromium.

Well I just did a chromium test of the source water supply and the reading was 3 ppb. Running though RODI it’s 12 pp. I guess for me it’s adding in 96%. some things just make zero sense.

Opus · Feb 13, 2020

ChadmRoman said:
Well I just did a chromium test of the source water supply and the reading was 3 ppb. Running though RODI it’s 12 pp. I guess for me it’s adding in 96%. some things just make zero sense.

That seems to be in line with your cities last water report. I would test after the carbon filter and then after the ro membrane and see what you get.

dankaqua · Feb 13, 2020

There is an ICP test which allows you to send in your RO water along with your tanks water:

ATI ICP-OES Complete Saltwater Water Test Kit

The results take longer to come back (from Germany) but it could give you more insights to the problem.

ChadmRoman · Feb 13, 2020

Opus said:
That seems to be in line with your cities last water report. I would test after the carbon filter and then after the ro membrane and see what you get.

After Carbon - 5
After RO Membrane only - 0
After Carbon RO Membrane (all four stages) - 6, yesterday 12 consistently over multiple tests
does this mean both are bad and I should replace?

Opus · Feb 13, 2020

I'm really confused on this one. It looks like your DI is releasing chromium back into the water. Not sure how that is possible if chromium is never making it past the RO membrane. I'm not sure how the DI material is processed/made so maybe chromium is used in that process? Maybe you got a tainted batch of DI?

I would suggest getting a new batch of DI from a different source than where you got your current one. See if that gets you to 0 chromium.

ChadmRoman · Feb 13, 2020

Opus said:
I'm really confused on this one. It looks like your DI is releasing chromium back into the water. Not sure how that is possible if chromium is never making it past the RO membrane. I'm not sure how the DI material is processed/made so maybe chromium is used in that process? Maybe you got a tainted batch of DI?

I would suggest getting a new batch of DI from a different source than where you got your current one. See if that gets you to 0 chromium.

you're not the only one confused, Dave over at Aquatic Life is just as stumped as both you and I. He's reaching out to the vendor of the DI solution for your exact questions. More to come I guess...

Opus · Feb 13, 2020

ChadmRoman said:
you're not the only one confused, Dave over at Aquatic Life is just as stumped as both you and I. He's reaching out to the vendor of the DI solution for your exact questions. More to come I guess...

Be sure to let us know if you find anything out. We always talk about 0 tds water, but there are things in 0 tds water that could still be harmful.

purp · Feb 13, 2020

or, just a thought, the measurement is off. is the chromium checker meant for marine water? im always wary of ICP data....

Randy Holmes-Farley · Feb 13, 2020

ChadmRoman said:
Well I just did a chromium test of the source water supply and the reading was 3 ppb. Running though RODI it’s 12 pp. I guess for me it’s adding in 96%. some things just make zero sense.

You sure no metal parts of any kind are in the ro/di collection, like a pump, hose clamp, etc?

the fact that there is a little bit in the source water does not mean that is the source.

Might also be testing error. There is at least one icp company I do not have confidence in.

An ro/di that is dropping tds to zero ppm from a much higher level will easily remove Chromium to at least the same extent as the other ions that comprise the tds.

ChadmRoman · Feb 13, 2020

purp said:
or, just a thought, the measurement is off. is the chromium checker meant for marine water? im always wary of ICP data....

Yes did a test of rodi and a fresh mix with TM Pro and both results were 12 ppb. Dave also confirmed with Hanna the checker is for both marine and fresh water.

ChadmRoman · Feb 13, 2020

Randy Holmes-Farley said:
You sure no metal parts of any kind are in the ro/di collection, like a pump, hose clamp, etc?

yes checked and everything collection cup is plastic. I did the tests directly into a glass cup, all results the same.
yesterday collection cup, direct into glass, and fresh mix of TM Pro al 12 ppb.
today
Source - 3 ppb
Test After Carbon - 5
Test After RO Membrane only - 0
Test After Carbon RO Membrane (all four stages) - 6
Could the DI cartridge increase chromium?
Also the icp is tritons and matches the results from the Hanna checker.

ChadmRoman · Feb 15, 2020

Just to provide an update. Started reviewing the setup of the RODI system and booster pump. Ran different test with different pressure and found if the pressure's above 65 PSI, there's chromium showing up in the storage tanks. With the pressure set to 65 or less, the results show zero chromium. Continuing to test, but I think I figured it out.

aerofly0610 · Feb 15, 2020

Can you put your tanks after the RO but before the DI? That’s how I run mine. But then again I have the RO piped to my fridge and bar. Then DI it before going to reef. But sounds like you have contaminated tanks.

Randy Holmes-Farley · Feb 16, 2020

I’m not sure how the pressure is having that effect unless you are pushing water through a defect (like a pinhole in the membrane).

In any case, it sounds positive that you have a way around it.

dankaqua · Feb 16, 2020

Randy Holmes-Farley said:
I’m not sure how the pressure is having that effect unless you are pushing water through a defect (like a pinhole in the membrane).

In any case, it sounds positive that you have a way around it.

Could the contact time inside the DI bed be a factor? If a pressure above 65psi is letting chromium through, but a lower flow rate is catching it, maybe the DI beads are already bound to another ion and it takes time to release X then catch the chromium?

(no surprise if I'm totally wrong given my very poor reef chemistry comprehension.... but I'm working on it... )

Randy Holmes-Farley · Feb 17, 2020

dankaqua said:
Could the contact time inside the DI bed be a factor? If a pressure above 65psi is letting chromium through, but a lower flow rate is catching it, maybe the DI beads are already bound to another ion and it takes time to release X then catch the chromium?

(no surprise if I'm totally wrong given my very poor reef chemistry comprehension.... but I'm working on it... )

That’s a possibility, but I would have expected to see such an effect on tds as well.