High Silicon in RODI Water

Poi Dog · Aug 13, 2020

Hello, looking for some help. I received my ATI ICP test back and it showed that my RODI water had high Silicon 44.40 ug/l versus a reference of 0. My handheld TDS shows 0. The sample was taken from a holding container that is a "food safe" dog food container. Any idea how this could happen and its effect on coral? I am having some issues with my SPS lately. The odd thing is my tanks Silicon is 74.72 ug/l versus the reference of 109.7 ug/l, under the reference.

minus9 · Aug 13, 2020

You can have silicate in your RO and still show zero tds. How many stages is your unit? Carbon blocks? DI resin(s)? Having multiple DI stages will help remove them.

Randy Holmes-Farley · Aug 13, 2020

Silicate is one of the easiest ions to get past a DI, especially if it is starting to deplete.

That said, do you have a significant problem with diatoms?

Don't let the number alone scare you. That's a huge issue with getting ICP tests. There's no reason to be concerned with it unless you have problem diatoms. I dosed way more than this to my tank intentionally.

If you use that water to replace 1% of the tank volume each day to replace evaporation, you are adding 0.4 ppb silicon each day.

When i dosed silicate, I typically dosed about 200 ppb once a week or so.

taricha · Aug 13, 2020

Poi Dog said:
RODI water had high Silicon 44.40 ug/l versus a reference of 0. My handheld TDS shows 0. ...
Any idea how this could happen and its effect on coral? I am having some issues with my SPS lately. The odd thing is my tanks Silicon is 74.72 ug/l versus the reference of 109.7 ug/l, under the reference.

0.04ppm Si may be "high" for RODI water, but it's not high for a system.
Hence the 0.11ppm Si "reference level" for tank water.
At those levels you might get some slight diatom growth but nothing that would cause coral issues.

piranhaman00 · Aug 13, 2020

TDS meters report ppm, 44.40 ppb will not be measured. I would not worry regardless.

Poi Dog · Aug 13, 2020

Thank you all for your responses, I appreciate your time.

@minus9 – My RODI has 1 sediment, 2 chloramine busters, 1 0.5 micron carbon block and 2 DI stages. All have recently been changed/refilled. I’m just surprised that anything has gotten through. I suspected a chloramine issue hence the focus on the chloramine busters. I’m thinking of sending a sample in directly from the unit since the tested sample came from the storage container. Although the storage container is only 3 gallons and is frequently refilled.

@Randy Holmes-Farley & @taricha – no diatom issues (knock on wood). I’m pretty good with water changes (30g every other week, total tank volume of ~150g). I also run a UV sterilizer.

The ICP results from the tank showed a high level of Barium (68.82 ug/l vs. reference of 10.97 ug/l) and tin (15.34 ug/l vs. reference of 0.55 ug/l). Do you guys think these levels would impact SPS? All of the parameters (Alk, CA, PO4, NO3, Mg, salinity) are tested weekly and are within normal levels. Although phosphorus tested low (2.26ug/l vs. reference of 16.46 ug/l), just started dosing Seachem Flourish.

taricha · Aug 13, 2020

That is a low P reading. If you have a good PO4 tester - does it agree? If not, I'd trust that over what they find in your water after several days of shipping, for something as reactive as PO4.

Randy Holmes-Farley · Aug 13, 2020

Poi Dog said:
The ICP results from the tank showed a high level of Barium (68.82 ug/l vs. reference of 10.97 ug/l) and tin (15.34 ug/l vs. reference of 0.55 ug/l). Do you guys think these levels would impact SPS? All of the parameters (Alk, CA, PO4, NO3, Mg, salinity) are tested weekly and are within normal levels. Although phosphorus tested low (2.26ug/l vs. reference of 16.46 ug/l), just started dosing Seachem Flourish.

I don't think those levels of barium or tin are concerning unless you already perceive a problem.

Tin is especially hard to judge as there are many different forms with different toxicity, but I've not seen folks have issues at that level.

Poi Dog · Aug 13, 2020

@taricha I have an old school hanna 93713 of which I get readings between 0.02 mg/l - 0.03 mg/l. The ICP result for phosphate was 0.01 mg/l versus 0.05 mg/l benchmark. So, it seems to be correct. I’m not sure how to test phosphorus or it’s relationship to phosphate.

@Randy Holmes-Farley thank you for the response. Still on the search for what is bothering my SPS. I don’t see anything else on the ICP that would be concerning, which is maddening.