Evaluating the Repeatability and Differences between ICP Tests

[Dan_P]

I think we all are running survivorship biased experiments - we end up with great tanks of the stuff that can handle how we reef and forget about all the stuff that dies with our style of reefkeeping.
When we say "show me your tank" it should be followed up with "beautiful! now show me your drawer of the casualties that didn't survive your tank."
Anyway, If you sent an ICP every 3 weeks and assumed whatever you got back was accurate and adjusted all those >1ppm elements in the charts above by however much ICP said those elements had changed, I don't think the swings would be fatal to anything, probably not even harmful. The worst case scenario here is you swing your Br, Sr, B 20-50% once every 3 weeks. I don't envision anything getting killed off by that.
But that's just a made up guess.

Thanks. Great insight into our bias. There is probably confirmation bias as well.

 

[taricha]

This is a slice of data that I think is interesting...
The first chart is how ICP did on the hobby-testable <1 ppm elements : Silicon, Iodine, Phosphorus.
The second chart is for what I call "well-behaved" ICP elements in the same concentration ranges as the first chart.
Concentration clearly isn't the only factor determining how well we might expect ICP to do. Some elements are easier than others.

Again Blue, Red, and yellow are vendors A, B, C with +-2stdev of each vendor shown. Black is +-2stdev across all vendors. And Gray is the comparison +-2stdev across 5 vendors from Sanjay's 7/12/23 article.
the average values across the vendors is shown in the top of the chart Si = 227 ppb, Iodine = 134, P = 25ppb.
Sometimes a vendor will have repeatable results, and sometimes 2 vendors have repeatable agreeable results (Iodine, vendors A and B) - but the overall picture is high variation - within or across vendors for these elements.


It's an interesting comparison to some "well-behaved" ICP elements in the same range...

Lithium* is far better measured than Silicon at the same concentration ranges, Mo and Ni are far better measured by ICP at much lower concentrations than Iodine and Phosphorus are. Barium's included as it is often a well-measured ICP element, and each vendor was consistent but did not agree with each other trying to measure a ~4ppb Ba level.

* (the huge +-2stdev from Sanjays 7/12/23 data is because ICP-analysis reported 0.0 lithium when everyone else said it was several hundred ppb.)

Not to beat a dead horse (we did a whole exercise on this premise) but it is interesting that the elements in this <1ppm range that ICP is the worst at are ones that we can run hobby tests calibrated against standards and get confident answers on.

But there are other ICP elements in the same range that ICP is much better at. And just because ICP largely sucks at telling you what your phosphorus or iodine is, doesn't mean that it isn't giving good results for Mo or Ni.

If I circle back to Dan's question here....

If I use ICP test results to judge how much element to dose or whether to fix an ion imbalance, would you think the uncertainty in the ICP result would cause me to really screw things up or would it be more likely a “so what” event for my fish and coral?

It is my opinion that if you used only ICP results to monitor and maintain Phosphorus at a target 0.05ppm PO4, I think there's a decent possibility you screw things up.
At ~1ppm PO4, it doesn't matter.

 

[Dan_P]

This is a slice of data that I think is interesting...
The first chart is how ICP did on the hobby-testable <1 ppm elements : Silicon, Iodine, Phosphorus.
The second chart is for what I call "well-behaved" ICP elements in the same concentration ranges as the first chart.
Concentration clearly isn't the only factor determining how well we might expect ICP to do. Some elements are easier than others.

Again Blue, Red, and yellow are vendors A, B, C with +-2stdev of each vendor shown. Black is +-2stdev across all vendors. And Gray is the comparison +-2stdev across 5 vendors from Sanjay's 7/12/23 article.
the average values across the vendors is shown in the top of the chart Si = 227 ppb, Iodine = 134, P = 25ppb.
Sometimes a vendor will have repeatable results, and sometimes 2 vendors have repeatable agreeable results (Iodine, vendors A and B) - but the overall picture is high variation - within or across vendors for these elements.


It's an interesting comparison to some "well-behaved" ICP elements in the same range...

Lithium* is far better measured than Silicon at the same concentration ranges, Mo and Ni are far better measured by ICP at much lower concentrations than Iodine and Phosphorus are. Barium's included as it is often a well-measured ICP element, and each vendor was consistent but did not agree with each other trying to measure a ~4ppb Ba level.

* (the huge +-2stdev from Sanjays 7/12/23 data is because ICP-analysis reported 0.0 lithium when everyone else said it was several hundred ppb.)

Not to beat a dead horse (we did a whole exercise on this premise) but it is interesting that the elements in this <1ppm range that ICP is the worst at are ones that we can run hobby tests calibrated against standards and get confident answers on.

But there are other ICP elements in the same range that ICP is much better at. And just because ICP largely sucks at telling you what your phosphorus or iodine is, doesn't mean that it isn't giving good results for Mo or Ni.

If I circle back to Dan's question here....

It is my opinion that if you used only ICP results to monitor and maintain Phosphorus at a target 0.05ppm PO4, I think there's a decent possibility you screw things up.
At ~1ppm PO4, it doesn't matter.

Thanks for this look.

You have just about motivated me to generate random ICP results for dosing decisions for a fictitious aquarium and see what happens over time for various scenarios of element depletion rates.