I have been consistently right around 4 ppm of free nitrate and .05 ppm free phosphate each morning now. After Dosing .5 ppm of nitrate (1ml of solution) I wait and hour and re test and get somewhere between 8 and 12 ppm after 1 hour. The numbers don’t really match up but it’s not reading excessively high. The Red Sea pro nitrate test kit is not very granular but seems consistent.
As I said earlier, brightwell says to wait 24 hours to measure. I do not know what the reason for this is, but I am assuming it is a good one. And probably explains your discrepancy in testing.