Next time don't add CYA. If you have ammonia is will be neutralized faster if no CYA is present. Then you just SLAM at 10-15ppm FC. There's no reliable way to predict when CYA will be converted to ammonia as it requires the presence of certain bacteria in the water. The presence of debris and earthworms tells me your pool got really dirty. A green/dirty pool is more likely to see ammonia issues. Sent from my iPhone using Tapatalk

My question: how can I prevent this from happening again next year?? Click to expand... I do feel those in the north can to some degree avoid ammonia by ensuring they close with adequate free chlorine, closing clean and cold, and opening cold. Eg take the pool to slam level, let drift down a day or two, then close/cover. If you open while water is in 50s, you will normally still have FC value. The conversion only happens after FC has zeroed out. If you open with a residual FC, you are highly unlikely to have it. While ammonia is one thing that causes the behavior you're seeing, I have a reasonable suspicion that excess antifreeze also causes similar symptoms for those in the north who close. If you use antifreeze when you close, always filter to waste to pump it off for a few minutes on opening. Just wanted you to know there could be an alternate thing at work.