ICP versus Hanna

[JulesH]

Hi

I was wondering if you could comment on a query I am having with my ICP test results.

I normally use a Hanna checker, the ultra low range phosphorus variety. I also use the standards that are available for this instrument, so I am reasonably sure I am getting a valid result from my checker.

That is until I looked at my recent ICP test. Accordingly I have a phosphate level of 0.28 mg/l where my Hanna checkers give me a range of between 0.05 to 0.02 mg/l an order of magnitude different.

I have a mixed reef tank with one fish. Would you have any idea why there would be such a large discrepancy before I take any remedial action please.

I am also aware of the accuracy/precision difference of the two instruments.

I would very much appreciate your thoughts.

Julian

 

[taricha]

A couple of thoughts.
One, make sure that you are reading the same units, and comparing phosphate to phosphate or phosphorus to phosphorus.
Two, you might want to watch a video of the technique with the hanna phosphate test and make sure you are doing it as expected. I've assumed that everybody does it the normal way, but have seen some people explain what they do and... well, chemical test technique can be important.
Three, Most ICP companies do an okay job on phosphorus, but I've seen "ICP-Analysis" totally blow phosphorus (both directions, high and low) in multiple samples.
Four, phosphate is one area where arguably it's quite challenging for ICP, but much easier with a chemical test. So in general, once I check for silly errors, I will trust a real-time chemical phosphate test over a shipped ICP phosphorus result.

 

[Randy Holmes-Farley]

I normally use a Hanna checker, the ultra low range phosphorus variety. I also use the standards that are available for this instrument, so I am reasonably sure I am getting a valid result from my checker.

Which ICP company? Not all are reliable, IMO.

When you say you use a standard, do you mean that colored water vials from Hanna? That is not a useful test of the accuracy of the answers. it is just a check on the electronics, not any sort of validation of the reagents, procedures, or vials used.

While I do not know what caused this difference, there is no reason that an ICP test for P must match a kit test of orthophosphate because they are measuring different things. There are many types of P in reef aquaria that will not show on a normal test kit.

That said, it is more likely that one or both of the values are off than that you do have high levels of these other forms of P (any organic form, such as phospholipids, DNA, RNA, whole bacteria,,, and certain inorganic forms as well).

 

[JulesH]

Which ICP company? Not all are reliable, IMO.

When you say you use a standard, do you mean that colored water vials from Hanna? That is not a useful test of the accuracy of the answers. it is just a check on the electronics, not any sort of validation of the reagents, procedures, or vials used.

While I do not know what caused this difference, there is no reason that an ICP test for P must match a kit test of orthophosphate because they are measuring different things. There are many types of P in reef aquaria that will not show on a normal test kit.

That said, it is more likely that one or both of the values are off than that you do have high levels of these other forms of P (any organic form, such as phospholipids, DNA, RNA, whole bacteria,,, and certain inorganic forms as well).

Hi Randy

Thank you for the reply. The ICP test was performed by a new(ish) company here in the UK, Reef Zlements. The Standards are the coloured waters. I understand they are not a validation of the reagents, vials used etc and specifically to tell me the device is functioning as expected.

I have attached the ICP companies response for your perusal.

 

[Randy Holmes-Farley]

The testing differences explanation they gave reflects what I said above, but it would be very unusual, IMO, to have that much organic P. Maybe they did not remove whole bacteria and other microorganisms from the water before testing.

IF that was the explanation, water changes would reduce it, but I'm not sure there is a rationale to do it just because it is high.

DO you use any organic export methods? GAC, Purigen, skimming, etc?

Yellow water would indicated a lot of organics (unless you use an oxidizer such as ozone which may remove color without reducing the organics that much).

 

[JulesH]

I have quite a simple set up, one Clarissa filter roller, bio balls, I use carbon and ROWAphos in the sump. The tank is mixed reef with one fish, a small red scooter blenny. I feed my LPS once a week, the fish gets a tiny amount of food or feeds on the abundant copepod population.

I have not noticed any yellow tinge to the old water after a water change.

 

[Randy Holmes-Farley]

I have quite a simple set up, one Clarissa filter roller, bio balls, I use carbon and ROWAphos in the sump. The tank is mixed reef with one fish, a small red scooter blenny. I feed my LPS once a week, the fish gets a tiny amount of food or feeds on the abundant copepod population.

I have not noticed any yellow tinge to the old water after a water change.

Then my expectation is that you do not have enough organic P to explain the higher ICP result, despite it being a viable theoretical explanation.

 

[JulesH]

Then my expectation is that you do not have enough organic P to explain the higher ICP result, despite it being a viable theoretical explanation.

Thats really interesting, I want to get my head around that, thanks Randy.

 

[Dan_P]

I am also aware of the accuracy/precision difference of the two instruments.

This is a late addition to some great answers to your question. While @taricha mentioned that ICP does pretty good with phosphorous, keep in mind that no ICP vendors informs us about the accuracy nor the precision of their test. Hanna does. @Randy Holmes-Farley points out the possible reasons for the difference between an ICP and Hanna phosphorous test results, but plain old experimental variation is always likely for an inexpensive ICP test.