Phos on ICP super high, not consistent with Hanna

[TunaC]

Tank is about 9 mo old.

Everything is stable/within normal limits EXCEPT phos which I have mostly under control but I have been testing about 2x a week to make sure I'm not letting it get crazy. (A few months back I had been feeding like a crazy person.) Range on the Hanna is .06-.17 for the last few weeks, so I was feeling pretty good about myself. I've been sending ICP tests (triton) monthly. Just got back October's result: Phosphate 1.089!

I rechecked on my hanna just now (happened to use a new batch of reagent as well as I just ran out of the old LOT) and got a whopping 0.16. My feedings have been minimal, my hanna tests over the last few weeks have been quite consistent, I don't believe my phos is as high as the ICP says.
I think I'm just going to carry on carrying on and not trust the test, maybe repeat now vs just wait until November, but wanted to see if anyone else had issues like this or any comments.

Corals are about as happy as I think they can be, fish are great aside from a carpet surfing Wrasse.

Cheers reefers.

 

[Christoph]

We occasionally encounter tanks with high total phosphorus levels, as measured by ICP (converting into mg/L concentrations when calculated as phosphate), but at the same time, they show low (or even undetectable) levels of reactive orthophosphate.

Unfortunately, we have not yet been able to identify this unknown phosphorus compound, nor have we determined its source. Without knowing the exact chemical species, it is impossible to assess its bioavailability or its potential to break down into phosphate. Initially, I suspected polyphosphates from the water source, but this has not been the case.

This highlights that it is not always a reliable strategy to assume that (almost) every phosphorus atom in the sample is present as phosphate, or to calculate phosphate concentrations based on an ICP total phosphorus measurement.

Best regards,
Christoph

 

[TunaC]

Interesting. My prior ICPs have been in line w Hanna home tests (and never crazy high). I’m inclined to repeating it now.

 

[TunaC]

Interesting. My prior ICPs have been in line w Hanna home tests (and never crazy high). I’m inclined to repeating it

 

[Randy Holmes-Farley]

We occasionally encounter tanks with high total phosphorus levels, as measured by ICP (converting into mg/L concentrations when calculated as phosphate), but at the same time, they show low (or even undetectable) levels of reactive orthophosphate.

Unfortunately, we have not yet been able to identify this unknown phosphorus compound, nor have we determined its source. Without knowing the exact chemical species, it is impossible to assess its bioavailability or its potential to break down into phosphate. Initially, I suspected polyphosphates from the water source, but this has not been the case.

This highlights that it is not always a reliable strategy to assume that (almost) every phosphorus atom in the sample is present as phosphate, or to calculate phosphate concentrations based on an ICP total phosphorus measurement.

Best regards,
Christoph

Thanks, Christoph. I agree that they need not match since they measure different things.

How did you rule out polyphosphates? Tripolyphosphate is a fairly common chemical that may be put into foods.

 

[Christoph]

Hi Randy,

i did not rule out polyphosphates from feeds - i have to think how this might could be done. Do you have something in mind? Might be best to rinse the feeds with D2O and run 31P NMR.

We just ruled out polyphosphates in the source water (which might be added there by the water suppliers to reduce precipitation/crusting of earth alkaline salts) - no elevated phosphorus levels in the source water.

all the best,
Christoph

 

[rishma]

Maybe obvious, but…
Do polyphosphates not show up on Hanna phosphorus checker?
Are polyphosphates not used by algae, bacteria, etc?

 

[Randy Holmes-Farley]

Maybe obvious, but…
Do polyphosphates not show up on Hanna phosphorus checker?
Are polyphosphates not used by algae, bacteria, etc?

They would generally need to be broken down into individual phosphate ions to be detected on hobby kits, which is done in the Hach total P kit with a tedious digestion step.

Bioavailability depends on what exact structure we are talking about, and whether the organism in question can chop it up.

 

[ReneReef]

Maybe obvious, but…
Do polyphosphates not show up on Hanna phosphorus checker?
Are polyphosphates not used by algae, bacteria, etc?

As far as I know, the phosphorus checker uses the same ascorbic acid method as the phosphate checker.
Only difference, is how the result is calculated and presented by the device.

The ascorbic acid method detects (ortho)phosphate, not total phosphorus. It does not break down polyphosphates.

 

[TunaC]

I just got back my repeat ICP test, send two weeks after what I am now certain was a fluke test. Phosphate is 0.024 (home hanna tests have been around 0.1). This is in line with what it has been recently, and although my hanna tests are a little higher than the ICP this go around everything seems consistent so I am happy and trust it. Not sure how I got a single ICP test with a phos level above 1. Good reminder to always question the data, even from a "reliable" test like ICP. Could've been something I did collecting the water from my tank (not sure what that would even be) or could have been some error at the lab. Whatever. Glad it's sorted.