I must be doing something wrong. I am using the TF-100 test kit. I have watched the videos and tried different light conditions. The CYA level was at 20 ppm, then I added 33 oz of cya. A week later the test showed 30 ppm. I took a sample to the pool store and they says it was 60 ppm. Then I added 16 oz of cya and after two weeks later the test shows 30 ppm. I will take a sample to a couple of different stores and compare. What could I be doing wrong performing the test?