Phosphate testing

[Reefer1978]

I am running into an odd issue with testing phosphate with Hanna Phosphorus Ultra-Low Range Checker (HI736). A few months ago I received a new pack of reagents, and my Phosphorus reading was getting lower and lower, until is stabilized at 16 ppb (about 0.05 ppm). I wasn't too concerned at this stage, figured I must be doing something right. But, cyano started showing up at some point, which got me concerned.

I sent away ICP test, (Triton), which confirmed my suspicion that Phosphate is indeed higher then Hanna is recording: ICP returned on July 2nd with:
* Phosphorus 96.00 µg/l
* Phosphate 0.294 mg/l

I contacted Hanna Instruments team who right away suggested it may be a bad batch, and sent me replacement reagents. They came in last week, new water test gave exact same reading as before --- 16 ppb (about 0.05 ppm).

Who do I trust?

 

[Dan_P]

I am running into an odd issue with testing phosphate with Hanna Phosphorus Ultra-Low Range Checker (HI736). A few months ago I received a new pack of reagents, and my Phosphorus reading was getting lower and lower, until is stabilized at 16 ppb (about 0.05 ppm). I wasn't too concerned at this stage, figured I must be doing something right. But, cyano started showing up at some point, which got me concerned.

I sent away ICP test, (Triton), which confirmed my suspicion that Phosphate is indeed higher then Hanna is recording: ICP returned on July 2nd with:
* Phosphorus 96.00 µg/l
* Phosphate 0.294 mg/l

I contacted Hanna Instruments team who right away suggested it may be a bad batch, and sent me replacement reagents. They came in last week, new water test gave exact same reading as before --- 16 ppb (about 0.05 ppm).

Who do I trust?

Did Triton measure phosphate or assume the phosphorous it measured came from phosphate and multiplied 96 micrograms x (95/31)

 

[Reefer1978]

I am running into an odd issue with testing phosphate with Hanna Phosphorus Ultra-Low Range Checker (HI736). A few months ago I received a new pack of reagents, and my Phosphorus reading was getting lower and lower, until is stabilized at 16 ppb (about 0.05 ppm). I wasn't too concerned at this stage, figured I must be doing something right. But, cyano started showing up at some point, which got me concerned.

I sent away ICP test, (Triton), which confirmed my suspicion that Phosphate is indeed higher then Hanna is recording: ICP returned on July 2nd with:
* Phosphorus 96.00 µg/l
* Phosphate 0.294 mg/l

I contacted Hanna Instruments team who right away suggested it may be a bad batch, and sent me replacement reagents. They came in last week, new water test gave exact same reading as before --- 16 ppb (about 0.05 ppm).

Who do I trust?

Did Triton measure phosphate or assume the phosphorous it measured came from phosphate and multiplied 96 micrograms x (95/31)

They provide 2 different readings in the report, but I don’t know if it’s measured or derived.

 

[Dan_P]

They provide 2 different readings in the report, but I don’t know if it’s measured or derived.

Do the multiplication I provided and see if it matches. I didn’t have a calculation handy.

 

[Reefer1978]

They provide 2 different readings in the report, but I don’t know if it’s measured or derived.

Do the multiplication I provided and see if it matches. I didn’t have a calculation handy.

Yes it matches

 

[Dan_P]

Yes it matches

Thanks.

The ICP measures all forms of phosphorous. It is likely that your system has 96 μg/L phosphorous and little or no phosphate. The analytical discrepancy you observed is common.

 

[Reefer1978]

Thanks.

The ICP measures all forms of phosphorous. It is likely that your system has 96 μg/L phosphorous and little or no phosphate. The analytical discrepancy you observed is common.

But I am using phosphorus checker, shouldn’t they match? And what about cyano if there’s little or no phosphate?

 

[Dan_P]

But I am using phosphorus checker, shouldn’t they match? And what about cyano if there’s little or no phosphate?

The phosphorous Checker measures phosphate but reports the result as the amount of phosphorous.

Typically, the correlation between phosphate concentration and cyanobacteria growth is poor

 

[areefer01]

Also worth mentioning that:

• Hanna kits != Triton ICP
• Testing timeline - did you take Triton's ICP water sample and the manual Hanna sample at the same time, same location?
• Hanna's margin of error (accuracy) of ±5 ppb ±5% of reading at 25°C

The two results may be similar but I would not expect them to be exact. In my opinion.

 

[Reefer1978]

The phosphorous Checker measures phosphate but reports the result as the amount of phosphorous.

Typically, the correlation between phosphate concentration and cyanobacteria growth is poor

Thank you, I didn’t know that.

Also worth mentioning that:

• Hanna kits != Triton ICP
• Testing timeline - did you take Triton's ICP water sample and the manual Hanna sample at the same time, same location?
• Hanna's margin of error (accuracy) of ±5 ppb ±5% of reading at 25°C

The two results may be similar but I would not expect them to be exact. In my opinion.

My readings are way part 5% margin of error, and they were taken at the same time.

 

[TwelveL16]

The phosphorous Checker measures phosphate but reports the result as the amount of phosphorous.

Typically, the correlation between phosphate concentration and cyanobacteria growth is poor

Thank you, I didn’t know that.

Also worth mentioning that:

• Hanna kits != Triton ICP
• Testing timeline - did you take Triton's ICP water sample and the manual Hanna sample at the same time, same location?
• Hanna's margin of error (accuracy) of ±5 ppb ±5% of reading at 25°C

The two results may be similar but I would not expect them to be exact. In my opinion.

My readings are way part 5% margin of error, and they were taken at the same time.

My icp test was pretty spot on with my 1736. ICP was taken couple days before Dino’s developed. ICP test was 0.018. Dino’s developed and I started checking phos regularly 1736 was showing 0 maybe 4-5 days after ICP sample was taken.

Reef moonshiners MS ICP test.

 

[JonasRoman]

This exemplifies a subject I quite often talk about: ICP doesn't measure phosphate. It measures the phosphorus atoms, and then they assume that everything is coming from phosphate and calculate by multiplying by 3. This means that the estimate always is false high to some extent. The more organics, the more false high. According to my experience, as long as the water is reasonably clean from visible organics, there isn't that big difference though between the calculated and the true phosphate, so in your case, I would double-check the Hanna accuracy with a reference fluid. Then you know.
Another reasonable safe way to double check is also doing a manual po4 with for instance red sea pro. That is easy to read with very few error sources and will definitely give you tge answer if water is approx 0.05 or actually .2.

Jonas

 

[Reefer1978]

This exemplifies a subject I quite often talk about: ICP doesn't measure phosphate. It measures the phosphorus atoms, and then they assume that everything is coming from phosphate and calculate by multiplying by 3. This means that the estimate always is false high to some extent. The more organics, the more false high. According to my experience, as long as the water is reasonably clean from visible organics, there isn't that big difference though between the calculated and the true phosphate, so in your case, I would double-check the Hanna accuracy with a reference fluid. Then you know.
Another reasonable safe way to double check is also doing a manual po4 with for instance red sea pro. That is easy to read with very few error sources and will definitely give you tge answer if water is approx 0.05 or actually .2.

Jonas

I was actually just about to make another thread about phosphorus vs phosphate, as my high phosphorus reading is bothering me. I confirmed Hanna is accurate, by testing clean SW, and buying another pack of reagents, all seems normal there. I didn't go as far as getting another test kit, I should mention that.

My phosphate readings are wild. Here's a chart of my Hanna tests. The peak is when I change GFO. My current reading is .15, I am assuming GFO needs changing again soon.

 

[JonasRoman]

I was actually just about to make another thread about phosphorus vs phosphate, as my high phosphorus reading is bothering me. I confirmed Hanna is accurate, by testing clean SW, and buying another pack of reagents, all seems normal there. I didn't go as far as getting another test kit, I should mention that.

My phosphate readings are wild. Here's a chart of my Hanna tests. The peak is when I change GFO. My current reading is .15, I am assuming GFO needs changing again soon.

Then it's very unusual with that huge diff between home test and ICP. Could only be explained then buy either ICP is actually wrong, or you have a lot of organics making ICP OES calculation pointless and very wrong. It's a good case to show we should evaluate strange values.

To be sure Hanna is correct ( I also think it is in this case) you cant just measure on pure SW, as in this case Hanna is showing false low (If its hanna that is bad and ICP correct), meaning you cant just take a zero value from pure SW as an evidence your Hanna is correct. The best way is to let Hanna measure on a ref fluid, like that one from FM that is 0.2 ppm. If Hanna spot that reasonable, then we know that your ICP was really misleading you here, and that in turn could be either of 1) A true error from ICP 2) ICP is measure P correct but you have so much organics so the calculation of PO4 will be misleading.

Jonas

 

[Reeferbadness]

Regardless of the accuracy of your Hanna or ICP, i don't believe there is a strong correlation between a cyno outbreak and higher Phosphate. I went away for a month and my father inlaw must have overfed both of my 200g tanks (by a lot) causing Phos to go from 0.06 or so in both tanks to .60 and above .99 (highest readable phos with ULP Hanna tester). I slowly got both down over about 1 month and didn't have any algae outbreaks, cyno or even any die off with SPS with only an odd sps frag browning out. Both tanks are back to stable (.08 or so). The only major thing i noticed was that the ALK and Cal consumption went way down .... like almost 1/2 ... which leads me to believe that coral growth slowed a lot but that was about it. The lesson for me is: Don't freak out about Phos; If you're getting issues like cyno, it's likely flo or some other issue other than Phos. My $0.02

 

[Reefer1978]

Regardless of the accuracy of your Hanna or ICP, i don't believe there is a strong correlation between a cyno outbreak and higher Phosphate. I went away for a month and my father inlaw must have overfed both of my 200g tanks (by a lot) causing Phos to go from 0.06 or so in both tanks to .60 and above .99 (highest readable phos with ULP Hanna tester). I slowly got both down over about 1 month and didn't have any algae outbreaks, cyno or even any die off with SPS with only an odd sps frag browning out. Both tanks are back to stable (.08 or so). The only major thing i noticed was that the ALK and Cal consumption went way down .... like almost 1/2 ... which leads me to believe that coral growth slowed a lot but that was about it. The lesson for me is: Don't freak out about Phos; If you're getting issues like cyno, it's likely flo or some other issue other than Phos. My $0.02

There was a study published someplace that SPS grow faster at higher Po4 concentration (visual), but skeleton is less dense.

 

[Reefer1978]

@Randy Holmes-Farley apologies if this was covered elsewhere, I tried to find it and couldn't see good enough description.

What's the relationship between all forms of phosphorous, and phosphate? Is it ok to concentrate on phosphate only, or are high concentrations of phosphorous also harmful to coral?

 

[Randy Holmes-Farley Verified Community Expert]

@Randy Holmes-Farley apologies if this was covered elsewhere, I tried to find it and couldn't see good enough description.

What's the relationship between all forms of phosphorous, and phosphate? Is it ok to concentrate on phosphate only, or are high concentrations of phosphorous also harmful to coral?

Nearly all phosphorus (which is an element) in a reef tank is made up of various types of phosphate (including lots of different organic molecules and inorganic phosphate).

 

[Reefer1978]

Nearly all phosphorus (which is an element) in a reef tank is made up of various types of phosphate (including lots of different organic molecules and inorganic phosphate).

What confuses me - which ones matter for coral, which ones inhibit coral growth? I've seen recommendation to follow Hanna only, which if I understand correctly measures organic phosphorous? Is low phosphorous but high phosphate acceptable? My last ICP reading was Phosphorus - 96.00 µg/l, but Hanna still shows low numbers, and I am seeing dull colors in SPS.

 

[Miami Reef]

What confuses me - which ones matter for coral, which ones inhibit coral growth? I've seen recommendation to follow Hanna only, which if I understand correctly measures organic phosphorous? Is low phosphorous but high phosphate acceptable? My last ICP reading was Phosphorus - 96.00 µg/l, but Hanna still shows low numbers, and I am seeing dull colors in SPS.

Orthophosphate is the inorganic type, and all of our hobby kits test that one. It’s also the one that would potentially inhibit calcification.

Hanna tests orthophosphate, changes the value into phosphorus (still the same inorganic type), which can be converted back into phosphate ppm. It’s always using the inorganic form, and that’s fortunately the most prominent form in reef tanks and the most important to test IMO.

It’s just unit conversion, like changing mL to L or gram to kilograms.