I became a BBB user since July 1, and use 3 lb shocks and 2 tablet during past two months. the CYA level tested by a pool store was 100 ppm on July 4. my CYA test result using TF-100 was 40-50 on July 8. The CYA level keeps the same range of 40-50 using TF-100. I went to the pool store to purchase MA and let them test water, the CYA level became 28!!. I tested two days ago, it was still 40-50.
I think my test result is more reasonable since there is no rains during these days. Why their testing results changed that a lot?