Zinc in RODI

[ScottF]

My latest ICP-MS test from Oceamo shows 9.3 µg/l of zinc in my RODI water. I took the sample directly from the filter. The filter is sediment -> carbon -> carbon -> RO -> cation resin -> anion resin -> mixed bed -> silica buster. None of the color change DI resin are even 1/4 used. TDS meters read 0.

Where would the zinc be coming from? Could zinc really be making it through my RO membrane and 4 stages of DI resin? Testing error? How bad is zinc for a reef tank?

 

[Randy Holmes-Farley]

Was zinc elevated in the tank? The RO may be unimportant (real or not) if not elevated in tank. Zinc is a needed and consumed trace element.

What was the copper level in the RO water? (helps assess if brass is corroding)

You are sure there are no brass connections after the membrane? No RO solenoid controller after the membrane?

How exactly did you collect the RO water?

 

[ScottF]

Was zinc elevated in the tank? The RO may be unimportant (real or not) if not elevated in tank. Zinc is a needed and consumed trace element.

What was the copper level in the RO water? (helps assess if brass is corroding)

You are sure there are no brass connections after the membrane? No RO solenoid controller after the membrane?

How exactly did you collect the RO water?

Zinc was fine in the reef tank. It was actually a little low. There was no copper in the RO water. The only thing inline after the filter is a pressure switch for the booster pump and a little ball valve. I guess I could move the switch to before the filter.

The water was collected by removing the output side of the ball valve from the collection tank and filling the test tube directly from the ball valve. So the water was coming directly from the filter, through the pressure switch and ball valve.

 

[Christoph]

Hi Scott,

was the silicon elevated aswell? If yes, this indicates exhausted filters (DI). If zinc was the only contaminant found, a contamination from within the system (probes, valves, etc) are the only likely source.

However as randy stated, adding a little zinc in your topoff water does not cause any issues, since its consumed, and the amount added is likely lower compared to the amount youa re dosing intentionally for trace element dosing.

Hwever if you do very large water changes (or start a new tank), the contamination will matter (but is still not critical at sub 10 µg/l zinc).

all the best,
Christoph

 

[ScottF]

Hi Scott,

was the silicon elevated aswell? If yes, this indicates exhausted filters (DI). If zinc was the only contaminant found, a contamination from within the system (probes, valves, etc) are the only likely source.

However as randy stated, adding a little zinc in your topoff water does not cause any issues, since its consumed, and the amount added is likely lower compared to the amount youa re dosing intentionally for trace element dosing.

Hwever if you do very large water changes (or start a new tank), the contamination will matter (but is still not critical at sub 10 µg/l zinc).

all the best,
Christoph

Zinc was the only contaminant on the report. I do monthly ICP tests and this is the first time I've seen anything other than n n in the Osmose section.

I'll move the pressure switch for the booster pump to the input side of the filter from the output side and replace the ball valve with a new ball valve. Then wait and see what my next ICP-MS test shows.

 

[Randy Holmes-Farley]

Does the ball valve have metal parts?

 

[ScottF]

Does the ball valve have metal parts?

I don't think so, but who knows?

Ball valve:
Ball valve

 

[UncommonSense]

I'll move the pressure switch for the booster pump to the input side of the filter from the output side and replace the ball valve with a new ball valve.

Is this the RODI’s automatic shutoff valve? Or the booster pump’s pressure switch?

If it’s the latter, it should be on the RO product water line (RO membrane product output)! Placing it pre-RO membrane will cause the booster pump to never turn on!

 

[ScottF]

Is this the RODI’s automatic shutoff valve? Or the booster pump’s pressure switch?

If it’s the latter, it should be on the RO product water line (RO membrane product output)! Placing it pre-RO membrane will cause the booster pump to never turn on!

The booster pump. You are probably right. The 60-80 PSI is probably enough to shut it off. I'll just leave it as is, replace the ball valve because I have a bag of them and wait to see what the next ICP-MS test says.

Edit:
Though I could probably put it inline between the membrane and the first DI stage. I'll leave it as is for now though.

 

[UncommonSense]

Though I could probably put it inline between the membrane and the first DI stage. I'll leave it as is for now though

Oh it can absolutely go between RO and DI!

In fact, that’s exactly how mine’s plumbed, it lets me flush the system via the RO only, then flip to DI water production while continuously running the pump!


If your booster pump/pressure switch are from Aquatec, I seem to recall the factory preset on the switch being 40PSI… it is adjustable, but that factory preset seems to work well in conjunction with my RO system’s 40PSI automatic shutoff valve!


— if you installed the booster pump pressure switch pre-membrane, it would be seeing city water pressure (typically around 60PSI-ish) any time the filtration system was operating, thus leaving it in the “off” position consistently (booster pump not running when you try to make water)!

 

[ScottF]

Oh it can absolutely go between RO and DI!

In fact, that’s exactly how mine’s plumbed, it lets me flush the system via the RO only, then flip to DI water production while continuously running the pump!


If your booster pump/pressure switch are from Aquatec, I seem to recall the factory preset on the switch being 40PSI… it is adjustable, but that factory preset seems to work well in conjunction with my RO system’s 40PSI automatic shutoff valve!


— if you installed the booster pump pressure switch pre-membrane, it would be seeing city water pressure (typically around 60PSI-ish) any time the filtration system was operating, thus leaving it in the “off” position consistently (booster pump not running when you try to make water)!

Yeah. It's the Aquatec 8800 bundle that BRS sells. It's feeding a five stage Spectrapure with a BRS "Triple DI Saver" extra three stages added to it.

I plumbed the first three stages of the Spectrapure and the membrane. Then from the membrane to the triple DI saver. Then from there back to the final stage of the Spectrapure. Sediment -> Carbon -> Carbon -> RO Membrane ------> Cation resin -> Anion resin -> Mixed bed ------> Silica buster.

It would be easy enough to put the switch in the line that goes from the Spectrapure to the Triple DI Saver.