High copper in RODI water

TexasReefer82 · Jul 24, 2020

Looking for some advice here...

Last week I sent in an ATI ICP test for both my tank water as well as my RODI. The results unexpectedly came back with 36ppb copper in the RODI water (as well as 4ppb tin). Where could this copper have come from? I don't have copper plumbing in my home, and I've never detected copper before in either RO-only or RODI water from the same unit. The RO membrane itself is only a few months old and the DI Resin is not yet exhausted and still reading 0 TDS on the output.

Is this reading an error?

Could the membrane or DI Resin themselves be a source of copper? tin? How about the RO tubing or the plastic carboy that I use to store RODI water?

The tank itself came back with zero copper - which is interesting considering this is same RODI water that I'm using for top off and water changes. If it has 36ppb I would think that copper would accumulate in the tank. Does a reef tank actually consume that much copper as a trace element?

TriggerFinger · Jul 24, 2020

I would also assume it would show in your reef tank. You don’t happen to have a copper test kit to check the rodi water do you?

TexasReefer82 · Jul 24, 2020

TriggerFinger said:
I would also assume it would show in your reef tank. You don’t happen to have a copper test kit to check the rodi water do you?

I don't, I'm trying to get a local store to test my copper for me

Miller535 · Jul 24, 2020

I believe I recall Randy stating that the ICP for copper in RODI water was unreliable. But I can not recall why.

If it showed up as 0 in your tank, I would not worry about it and would call it testing error.

amps · Jul 24, 2020

Do you have any brass fittings you use after the RO membrane? I made that mistake once....

Randy Holmes-Farley · Jul 24, 2020

I suspect it is more likely it came after the RO/DI, not through it.

TexasReefer82 · Jul 24, 2020

No brass fittings whatsosever.

The only thing that has changed in the RODI system since previous testing was that I installed a saltwater mixing station consisting of additional 3/8" tubing and puch connect fittings, PVC pipe and schedule 80 fittings all from BRS and these polyethylene containers - linked below.

Ace Roto-Mold 20 Gallon Upright Rectangle Flat Bottom Tank | SP0020OM

Buy Den Hartog Ace Roto-Mold 20 Gallon Upright Rectangle Flat Bottom Tank | SP0020-OM - SP0020OM from Barndoor Ag.

barndoorag.com

Could this type of container contain copper??? I wouldn't think so but knows! haha

Randy Holmes-Farley · Jul 24, 2020

The PVC may be the source of the tin, but I don't see a source of the copper.

Was the sample 0 ppm TDS when you collected it for ATI?

Miller535 · Jul 24, 2020

Randy Holmes-Farley said:
The PVC may be the source of the tin, but I don't see a source of the copper.

Was the sample 0 ppm TDS when you collected it for ATI?

I may be wrong, but his post looks like it says he had copper in his RODI but NOT his display tank (according to ATI ICP). Which is why I thought testing error.

TexasReefer82 · Jul 24, 2020

Randy I agree I don't see a source for copper downstream of the DI Resin either.

Yes the sample was 0 TDS coming out of the DI resin. However, that small TDS meter only reads down to 1 ppm. I would think that a reading of 36 ppb is below the LOD and could pass undetected.

My current working hypothesis is that the copper came from the raw tap water (which in the past has tested as high as 20ppb). Perhaps there was recently a large increase in copper in the Houston Tap water. I suspect that it got through the RO membrane even though it's new and also got through the DI resin. This batch of DI resin isn't the typical stuff from Bulk Reef Supply - I picked it up from my LFS in a pinch a couple months ago, perhaps it's of a lower quality or perhaps this is the very beginnings of breakthrough that I'm observing. I don't know why the resin would selectively pass Copper over any other ion.

I think that the reason the tank itself read zero for copper is because 1) all top off water is quarter strength kalkwasser which would precipitate much of the copper and 2) copper is rapidly bound to organics and can be skimmed out or removed with GAC which have both been running. I feed the tank heavily with phytofeast, oysterfeast, AB+ easySPS and easyBOOSTER as well as feeding the fish - so there is plenty of organics around! haha

Here's the plan: I picked up a package of Cuprasorb and will treat the existing product water with it via a small media reactor. I will also replace this DI resin with the typical BRS product that I'm accustomed to using. I may also replace the membrane itself.

Any thoughts?

Randy Holmes-Farley · Jul 24, 2020

36 ppb would certainly be undetectable, but it would also be highly remarkable for copper to be the main ion in the effluent.

Since the tank shows none, I would not go to great lengths to remove it from the DI water since its rate of addition to the tank is low.

putting cuprisorb in the DI water storage seems unlikely to cause any issues and seems like a fine plan.

Pygmey · Feb 5, 2021

Any follow up on this? I received a test from ATI and they say I have copped in my RODI. I am testing it zero tds and putting directly in my testing tube. THey said I have 18 ug/l.. I bought a Hanna copper test kit. Tested with that and it said 0.08 ppm.. I have no idea where it would be coming from though.

Randy Holmes-Farley · Feb 5, 2021

Pygmey said:
Any follow up on this? I received a test from ATI and they say I have copped in my RODI. I am testing it zero tds and putting directly in my testing tube. THey said I have 18 ug/l.. I bought a Hanna copper test kit. Tested with that and it said 0.08 ppm.. I have no idea where it would be coming from though.

The Hanna appears unreliable for copper that low, but ATI should get it right by ICP.

What did the tank water come out as for copper?