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

[Aqua Man]

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]

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

https://www.hach.com/phosphate-standard-solution-1-mg-l-as-po4-nist-500-ml/product?id=7640201657

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]

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.

That’s where I got mine:-) I got suspicious when things did not work out.