I just got a solar cover this year and I might be crazy but I think it is creating something that is breaking down my CYA.
2x this year my pool has gone from stable to green. No need to preach as I have learned my lesson but I get in a habit of testing only FC and PH when things are going well. We have not been swimming much the past month and I have just left the solar cover on. All went well for 3 weeks, this past week I had some algae settling on the bottom an my FC dropped to 1 ppm. I added bleach to bring it back to 5 and ran the robot.
That angered the pool gods and now I am at 0 FC and all of my CYA has disappeared. This happened to me once earlier in the year as well.
Is it possible the solar cover is causing a problem? I can't imagine a reason for CYA to disappear other than ammonia but what would create that? And how can I test for it?
FYI I know how to fix it with stabilizer and SLAM just interested in how to prevent it and what on earth would create it.