Well, one thing that helped my original predicament. There wasn't much difference in appearance of the dot from 80ppm to 50ppm. So what I did was to test a new sample made up of 50% pool water and 50% tap water to dilute the sample and see how it went. Well this time it was much easier to read and the result seemed pretty conclusive at 40ppm (which unfortuneatly means that I am at 80ppm, too high). Anyway perhaps higher CYA numbers are harder to read than lower?