Testing a Hanna Phosphorus ULR Checker - Am I Missing Something?

Aqua Man · Jul 8, 2020

chipmunkofdoom2 said:
In general, this is going to be the rocks and sand, even if you only have a small amount of rock. Calcium carbonate has a very high capacity for binding phosphate relative to the concentrations we usually encounter in reef aquaria.

My tank is 6 yrs old. Very basic setup and have never used phosphate removal media.
One would think that my rocks should be loaded up by now!

chipmunkofdoom2 · Jul 8, 2020

Randy Holmes-Farley said:
It might be better to get a reliable phosphate standard than to have to be uncertain of the hydration level in the solid used:

Phosphate Standard Solution, 1 mg/L as PO4 (NIST), 500 mL

Phosphate Standard Solution, 1 mg/L as PO4 (NIST), 500 mL

www.hach.com

Thanks for the link. I was hoping to use the tools available. This may have to be my next step since if I can't get any clarity on the hydration of the Na3PO4 I'm using.

Dan_P · Jul 8, 2020

chipmunkofdoom2 said:
The numbers for hydrous Na3PO4, however, are a different story. These are much, much closer.

Na3PO4.H2O % PO4 = 30.97 / 137.99 = 22.44%
7.12g Na3PO4.H2O * 22.44% PO4 = 1.598g PO4
1.598g PO4 / 3.785 gallons = 0.42219 g/L = 422.19 mg/L = 422 ppm PO4

Na3PO4.H2O

Test Expected Concentration (PO4) Expected Reading (PPB) Actual Reading (PPB)
1
0.000
0
0
2
0.019
6
2
3
0.038
12
0
4
0.095
31
25
5
0.189
62
49

I will have to see what the vendor says. The supplement was sold by Loudwolf and was explicitly labeled as CAS 7601-54-9, which is anhydrous. I suppose it's possible it could be one of Na3PO4's various hydrates, although I'd be disappointed if it was and it wasn't labeled as such.