My cyanuric acid reading was very high this opening. Was advised to drain and refill (3/4 drain anyway) to dilute the CYA. First reading after refill was acceptable (60) so I brought all other things into balance. Second reading after refill was very high (130) and third reading 2 days later was off the charts again. After lots of checking with others, it was suggested that I need to brush the walls and flush with water continually when draining the pool. Apparently the CYA will attack to the plaster and reintroduce itself when the pool is refilled. Anyone have experience with this? I am about to go about it again and want to get the best result possible as water is quite spendy. Pool is 25,000 gal., inground concrete/plaster, 15x30.