there is a calibration step that fixes it, makes all titration kits work:
vs trying to believe/disbelieve your bottom end, the wastewater, measure only the change- that's what indicates the bac. not the debatable bottom end (the .25 vs zero debate)
change the tank water or polyfilter it in such a way that it is known zero ammonia, without a test kit. such as, 100% water change.
then take a reading, whatever the color is= zero
dose the tank using liquid AC meant for cycling like Dr Tims, to the first increment of free ammonia the test kit can register. not 2 ppm, the first increment of change it registers. half a ppm is fine, something that changes the test kit color barely.
wait 24 hours
retest ammonia and it w likely be back to the calibrated zero.
key takeaway=2 ppm not required, test kit that reads zero not required, mere detectable motion down from the + condition is proof of bac. By calibrating the color test against the forced zero ammonia condition, misreading isn't at play as long as Prime water conditioner isn't used at any step. if it is, all testing is null. Prime skews all api testing.