Difference in PPM, which one is correct?

[waterbear]

Ok, I've archived that. Do those instructions still apply to all current test strips?

Don't know but 5 discovered on my own thatn 5 minutes ofent ws not long enough for the liquid to travel to the top of the strip and turn the top dark with the older strips but when I gave it a full 10 minutes the srip would be on the money (at least pretty close in the ballpark) with a calibrated goldline (oakton) salt meter