My chemistry is fine. Chlorine 3.0, both free and total. but look at these pictures! These arrived overnight. It was not a windy night, and I have a pool screen. These guys are too big to come through the screen. This is a first for me, as a long time pool owner. I will use the net to skim them off....but thoughts on what happened here? Or how to prevent them from doing this again? (no rain, regular 60 degrees at night, 80s during the day. Pool water is 74 degrees. Any comments welcome. Thank you!