Phosphate testing

[JonasRoman]

I've ran into this a few times, my Hanna & Salifert results are always higher than what I get back on ICP. I'm no chemist but i've always had a suspicion that nutrients are getting consumed by the bacteria in the water on the 2 week ride to testing.

Doesn't matter if po4 is consumed as icp measure P, not po4, and thus is not sensitive to consumption of po4.

 

[BuffaloLake]

I have a 310 gallon system running the full Triton method. I have a Trident NP on the system, backed up by Hanna checkers. I had been getting wildly different results on the readings. So I recorded the Trident results, then ran 3 Hanna tests, then took a sample for an ICP. These are my readings from that test:
Trident NP 0.22
Hanna ULR Phosphate average 0.39
Triton ICP 0.07

Nitrate was also wildly different between Hanna and Trident. But I didn’t see nitrate listed on the ICP

Kinda at a loss on what I can trust.

ICP measures P not PO4. What was measured or reported?

Phosphorus came back 25.00

Phosphate at 0.077

Per Triton ICP

 

[BuffaloLake]

I have a 310 gallon system running the full Triton method. I have a Trident NP on the system, backed up by Hanna checkers. I had been getting wildly different results on the readings. So I recorded the Trident results, then ran 3 Hanna tests, then took a sample for an ICP. These are my readings from that test:
Trident NP 0.22
Hanna ULR Phosphate average 0.39
Triton ICP 0.07

Nitrate was also wildly different between Hanna and Trident. But I didn’t see nitrate listed on the ICP

Kinda at a loss on what I can trust.

ICP measures P not PO4. What was measured or reported?

 

[JonasRoman]

Phosphorus came back 25.00

Phosphate at 0.077

Per Triton ICP

PO4 is not measured by triton. It's just calculated from 25 ppb Phosphorus.

 

[Randy Holmes-Farley Verified Community Expert]

No Randy, Triton do not measure true po4 with photometry but P with icp and then calculate po4, so it shouldn't be time sensitive as they measure just P atoms, which can't dissappear/consumed.

If it gets into organisms or precipitates on the container walls, those would not make it to the icp plasma.

 

[EnterName]

If it gets into organisms or precipitates on the container walls, those would not make it to the icp plasma.

Never thought about that, but it makes sense... However, is there enough surface area on these plastic vials to actually reduce phosphate meaningfully?

... another good reason why these kits should probably include sterile filters.

 

[Randy Holmes-Farley Verified Community Expert]

Never thought about that, but it makes sense... However, is there enough surface area on these plastic vials to actually reduce phosphate meaningfully?

... another good reason why these kits should probably include sterile filters

I’ve never tried to quantitatively determine an answer to that.

 

[Dan_P]

Phosphorus came back 25.00

Phosphate at 0.077

Per Triton ICP

Thanks for the clarification.

 

[Dan_P]

I’ve never tried to quantitatively determine an answer to that.

You could monitor the PO4 concentration of a sterile sample of aquarium water in a plastic sample tube (15 mL centrifuge tube). To increase the surface area, add pieces of cut up plastic tube. I tried this several years ago but don’t recall what I observed. We had this discussion before when there were more experimenters online. This is where an AI agent would be helpful, recalling past conversations.

 

[EnterName]

Would be interesting to know if the ICP labs acidify their tubes prior to testing to avoid the precipitation issue and maybe even the potential biofilm growth on the tube walls.

Interestingly the effect on metals seems to be high enough that there are US regulations in place. US rules say a water sample may be shipped without acid preservation, but acid must be added at least 24 hours before analysis to dissolve any metals that adsorb to the container walls. (These regulations will not apply to aquarium samples, but it shows that this is a concern):

• https://www.deq.nc.gov/metals-epa-2008-checklist-pdf/open
• https://www.health.mn.gov/communities/environment/mnelap/docs/samplehold.pdf