PO4 Heat Test

[Dennis Cartier]

I recently ran across an interesting document on the Fauna Marin site. It deals with a method that they suggest can help test the amount of phosphate deposits that are bound to the substrate surfaces of the tank. This sounds like something that I could use as I have always wondered how much more bound phosphate has yet to be released while I am actively lowering PO4 with LaCl. When I am trying to lower my PO4 levels, I operate a LaCl reactor 24x7 over many months, until I get the PO4 slowly lowered back into my target range.

I performed the test this morning during my daily tests. I was expecting to see a very high result. The tank has been sitting at about 0.23 ppm recently. It is a bit higher today (0.248 ppm) as my LaCl reagent ran out sometime between Friday and Saturday afternoon, when I noticed it and replenished it.

Heat Test 91 ppb / Normal test 81 ppb = 1.12 ratio

So my result shows very little released (bound) phosphate. Not what I was expecting to see. It's possible that my active 24x7 of LaCl may be impacting the result. I attempt to pull out the newly released, along with the daily added amount from food, fast enough to stay ahead of the increase and get a gradual decrease in phosphate as a result. If the test is being impacted by my use of LaCl, that actually might be even more useful to me, as it would provide feedback on matching my reduction process, compared to the release process of bound phosphate.

I would be interested to see anyone else's results, especially if you are not using phosphate absorbers currently. Also everyon'e view on the premise of this test.

The FM Heat Test document link is below:
https://www.faunamarin.de/wp-content/uploads/2021/04/FM_HTU_Hitzetest_EN_NEU_210421.pdf

 

[Randy Holmes-Farley]

What am I misunderstanding?

"Take a 0.2 l (200 ml) sample of aquarium water; use a glass cup. •Place the sample in the microwave and heat the water to near-boiling temperatures (94 – 96°C or 201 – 204°F), then wait 4 minutes for water to cool. • Take a water sample from this glass cup, then let it cool to room temperature. • Perform your PO4 test using this room temperature water sample and compare your results with the standard test method."

I don't follow the rationale/interpretation for this test at all.

There are no CaCO3 solid deposits in this test, right? Just water?

I also doubt having solid deposits in the heated sample would give the info stated (different discussion we can get into if needed), but how does heating the water tell you what is in a solid deposit that is not in the heated sample?

It seems to me this is a test for dissolved or finely suspended material that is not detected by a normal test, but is broken into orthophosphate by heat. That would include whole bacteria, dissolved organics that contain P, and some inorganic forms of phosphate such as polyphosphates.

 

[taricha]

I don't follow the rationale/interpretation for this test at all.

There are no CaCO3 solid deposits in this test, right? Just water?

So it's meant to make some form of Phosphorus (organic?) that wouldn't register as PO4 into testable PO4? Are there organic forms that would break down under just 100C heating?
Or maybe this is meant to disrupt cells and release some amount of PO4 that had previously been associated with cells?

 

[taricha]

but, yeah I don't see the connection to PO4 bound on calcified surfaces - if no surfaces are tested in any way.

 

[Dennis Cartier]

I guess the premise is that the amount of phosphate in the water column that is not orthophosphate is elevated by the amount of phosphate bound onto calcified surfaces.

That is why I was expecting to see a high result for my tank, but instead got a low result.

 

[Randy Holmes-Farley]

So it's meant to make some form of Phosphorus (organic?) that wouldn't register as PO4 into testable PO4? Are there organic forms that would break down under just 100C heating?
Or maybe this is meant to disrupt cells and release some amount of PO4 that had previously been associated with cells?

For sure. Many organic and inorganic forms break down faster with heat.

 

[Randy Holmes-Farley]

I guess the premise is that the amount of phosphate in the water column that is not orthophosphate is elevated by the amount of phosphate bound onto calcified surfaces.

That is why I was expecting to see a high result for my tank, but instead got a low result.

Why would that be the case?

This might be a useful test in some context, but I do not see how they conclude it has anything to do with bound ortho phosphate.

 

[Dan_P]

Why would that be the case?

This might be a useful test in some context, but I do not see how they conclude it has anything to do with bound ortho phosphate.

The Fauna-Marin article is a very confused one, composed by a home made Chatbot, or maybe just a poor English translation.

Anyway, boiling seawater for a short time would convert polyphosphate to phosphate, though I have no idea how quantitative the conversion is. The increase in the PO4 reading in the boiled water is the “depot” quantity contained in polyphosphate not the amount in the sand or rocks. I bet if @jda would boil some polyphosphate in tank water for us (he has some used in the recently aborted aragonite adsorption of PO4 experiment) we would have a demonstration of what Fauna-Marin is talking about.

 

[jda]

You want me to mix up some polyphosphate, test it, boil it and then test it again? Let me know the amount of water and metaphosphate to mix and I can do this. I guess we would have to mix the same amount in a different container and wait for a few days as control?

In my test, the polyphosphate slowly turned into orthophosphate over a three day period. I did not test by the hour, but after about 3 days, the po4 numbers stopped climbing on a hannah.

I have done a lot of research on this since. Most of the poly/meta in our tanks is fish/invert byproducts. They break down into ortho. Ortho does not usually turn into poly. I saw no indication of how long this took, but let's say 3 days from above. Several different forms of poly/meta are much preferred to ortho for phosphorous to be used as a build block by organic tissue and hosts. LaCl binds ortho only. GFO can bind both meta/poly and ortho. This could be why people see corals stress with GFO*, but not with LaCl since the meta/poly is still there for corals to use as the ortho gets removed. Most do not differentiate between ortho and poly, but the few that did seemed to indicate that ortho binds to aragonite/calcite/dolomite and not so much poly. Much of this has needed to be translated and I am not that smart, so there is a lot to unpack for me still. This has been incredibly hard for me to search since poly/meta/complex all seemed used interchangeably and even just "po4" is used sometimes even in publications when they differentiate the types in other places.

Do we even know if polyphosphates can bind to aragonite? I cannot test this since there is no way for me to know if the poly got bound, or if it bound once it converted to ortho.

* I am not talking about fish death from LaCl, just coral stress.

 

[Randy Holmes-Farley]

Do we even know if polyphosphates can bind to aragonite? I cannot test this since there is no way for me to know if the poly got bound, or if it bound once it converted to ortho.

They will, yes. Possibly more strongly than orthophosphate to a calcium carbonate surface. It will have more points of contact to the surface than orthophosphate.

 

[jda]

They will, yes. Possibly more strongly than orthophosphate to a calcium carbonate surface. It will have more points of contact to the surface than orthophosphate.

If the poly later breaks down, it is likely that the individual po4 that is bound to aragonite stays bound and the other po4 structures are free to roam, or just bind themselves since they are in close proximity? I don't imagine that there is any way to know what happens to the other things in the compounds in a breakdown?

 

[Randy Holmes-Farley]

If the poly later breaks down, it is likely that the individual po4 that is bound to aragonite stays bound and the other po4 structures are free to roam, or just bind themselves since they are in close proximity? I don't imagine that there is any way to know what happens to the other things in the compounds in a breakdown?

Tripolyphosphate itself breaks down to just orthophosphate. Same for cyclic trimetaphosphate and any linear polyphosphate.

Tripolyphosphate can act as a metal chelator, and if it breaks down while holding metal, it will likely release it.

Organic phosphates have a multitude of attachments of organics to the phosphate. The most unstable have more phosphate in a row, like ATP. Those release phosphate from the end, then more slowly the second one, then even more slowly, the last one, leaving an OH group on the organic.

There's a diagram of that here:

https://www.researchgate.net/figure/a-Steps-in-the-hydrolysis-of-ATP-to-adenosine-b-Structures-of-cyclic-phosphates_fig5_6873171

 

[taricha]

I tried this just for kicks. I didn't find much and I think it's a bit hard to interpret.
When I run my water up to just about boiling, I get noticeable cloudiness from precipitation.

(side by side Tank water vs heated in microwave. )

This makes the PO4 test difficult to interpret with a hanna checker. Because the heated sample registered as noticeably cloudy equal to ~50ppb Phosphorus before running the phosphorus test. So I compared all samples to a separate blank cuvette.

vial 1 & 2 (tank water duplicates)
before: 0, 0
after PO4 test: 5, 10 ppb

vial 3 & 4 (heated tank water duplicates)
before: 49, 57
after PO4 test: 40, 62

The acid in the hanna PO4 test could've dissolved some of the heat-induced precipitation - lowering the reading. Or the hanna test could've reacted with polyphosphates converted to PO4 and raised the reading. Since the reacted samples contained no detectable blue - it's hard to say much PO4 was found with or without heat.

For low values like this, it looks like it'd be really hard to interpret. If a heated sample went noticeably more blue - then yes I'd feel good about the increased reading being some detected additional forms of Phosphate - but that wasn't what happened in my water. They all stayed really colorless.


L to R: blank, vial 1, 2, 3 & 4 after reaction.

 

[Randy Holmes-Farley]

The precipitate is likely calcium carbonate. Heating reduces its solubility and drives off CO2, raising pH