Help me understand the relationship between phosphorus and phosphate

[Steve1500]

Below is the Triton ICP test results for P and PO4. Triton shows these as high.

Currently, my Hanna Phosphate LR checker shows .05-.06 ppm, however, when I took the sample, things may have been different.

Questions:
1) What is the difference between P and PO4 and what should I focus on?
2) How do I convert ug/l to ppm?
3) Should I do anything or trust my Hanna checker for the current values?

Nutrient-Group
Element Analysis Setpoint Deviation
P 42.00 µg/l 6.00 µg/l 36.00

PO4 0.129 mg/l 0.018 mg/l 0.111

 

[Christoph]

Hi Steve,

Phosphorus is "P" while phosphate is PO4. - Its easilly seen that also PO4 contains "P" together with some oxygen atoms "O". P can exist in many forms besides in phosphate (such as within DNA/RNA or many more molecules), but only (or mainly) the phosphate PO4 is bioavailable to corals.

ICP is just measuring P, and triton assumes that all P in the sample is actually phosphate (PO4). Unfortunately this assumption is not correct, so the ICP is overestimating phosphate usually by a good deal. To measure the phosphate-portion only you need a colorimetric test (such as Hanna).

To convert from P [µg/l] to PO4 [mg/l] multiply the value with 0.00306.

Hope that helps!

Best Christoph

 

[Steve1500]

Hi Steve,

Phosphorus is "P" while phosphate is PO4. - Its easilly seen that also PO4 contains "P" together with some oxygen atoms "O". P can exist in many forms besides in phosphate (such as within DNA/RNA or many more molecules), but only (or mainly) the phosphate PO4 is bioavailable to corals.

ICP is just measuring P, and triton assumes that all P in the sample is actually phosphate (PO4). Unfortunately this assumption is not correct, so the ICP is overestimating phosphate usually by a good deal. To measure the phosphate-portion only you need a colorimetric test (such as Hanna).

To convert from P [µg/l] to PO4 [mg/l] multiply the value with 0.00306.

Hope that helps!

Best Christoph

Thanks! It sure does help me understand.

 

[Scrubber_steve]

From Randy Holmes-Farley; Chemistry And The Aquarium: Phosphorus: Algae's Best Friend