Phosphate versus Phosphorus measurement

[nycman]

I have been using a Hanna tester to measure my phosphates for a year, and the result has always been 0.00. Recently, because of discrepancies between test kits on other parameters, I sent a sample of my tank water to ICP who test for 30 parameters and then post it on their website. They measure phosphorus, not phosphate, and had mine at 0.087, which translates to 0.276, which is very high. How can this be?

 

[Dan_P]

Our test kits only measure reactive or ortho phosphate, which is PO4.

There are many phosphorous compounds in the water that could be picked up by ICP. A total phosphorous measurement would likely be larger than a test kit value. I would contact the vendor and find out exactly how they measured phosphorous.

 

[nycman]

I think you are right. I went back to the site and you can compare all 30 elements that they test to ocean water in four locations. My 0.087 measure of phosphorus compares to 0.05 in Fiji, 0.07 Hawaii, 0.07 St Thomas, and 0.12 Florida. So it seems fine.