Anyone using Red Sea Phosphate test?

[asylumdown]

I've used it twice now, and to my eyes, the colour in the sample vile matches the 0.08ppm colour disc closest, but I tested two weeks apart, with several changes of GFO in between. My Hannah checker comes back at 0.00ppm.

Problem is the colour I get in my sample vile doesn't really exactly match any of the colour discs on the wheel of the Red Sea kit very well. Not bright or yellow enough to be 0, but not really green enough to be in the 0.08 and above class. Is that normal? I find their nitrate test to be bang on and super easy to interpret.