I would have to disagree with not having seasonal changes. I run an airline to my skimmer that goes outside so humidity levels are constantly changing. Also in the summer here in canada my tank goes up about 2 degrees even with chiller fans. Then back down in the winter. Not sure if that's enough but it could be a cue I guess.I was thinking the same thing since there really isn't seasonal changes in our tanks. They'd have to have a cue of some sort to initiate the seasonal die off. Saying that though, I've had zoas seemingly die off for no reason. Zoas are a PITA sometimes.