Mknauss, why is a CYA result of 2 not possible? As the chemical is added to the water feom 0 ppm it will be 2 ppm at some point. If you are referring to the resolution of a particular test method, I own and use a Pool Lab 1.0 photometer to test my water. Pool store test results matched my results exactly on all parameters from split sample. I was in the water bottling industry for 15 years and I am not a fan of certain reagent and titration tests when there are better more accurate methods. I used photometers extensively at work, and have found the Pool Lab to be quite accurate and repeatable.