Lower Mainland PO4 readings.
 

I have a salifert test kit for PO4, but the chart is so ambiguous you cannot tell between the first and third colors when looking at the test vial.

Does anyone have more accurate readings?

Have you tried doing the low range procedure by doubling all the reagents and test water then dividing by two?

Ya I tried, but it's so hard to determine whether it's clear or got a tint of blue. If it were any other color, but blue is too hard to distinguish.

Well, really sensitive kits are out there but they go for lots of $.