We use the TFP test kit that this cite recommends and my wife does the pool testing for consistency. Our CYA seems to fluctuate a lot. Sometimes its 50, then it could be 65 or if I add some stabilizer, it could be 70. But then it drops. We bought the test CYA solution that I saw mentioned on this cite (where you pour in the test solution instead of the actual pool water) and everytime she uses it, she gets 50 (which is what she is supposed to get). Thus, I think her testing of the CYA is accurate.
My question is should CYA be fluctuating with perhaps evaporation or PH movement? Our new Pool was just filled in June and PH does rise frequently, if that affects CYA.