I had 75 ppm of CYA in March and tested it again yesterday to find it was <15 ppm using Taylor K-2006 kit. I am confident in my test ability, but don't normally test CYA due to historical experience that once stable, it doesn't go away without water change. Like the others here, I am confident I do not have a leak or abnormal loss of water. I opened the pool on 4/15 and have kept it at 90 all summer, with one accidental day where my son turned it up to 100 (solar got us to 99 by the time I caught it). So I am thinking it may be heat/temp related as suggested earlier here?