Mine do the same thing. I tried searching the net for answers about it but there doesn't seem to much on that particular subject of Anenomes. Usually they do it when I turn out the main lights, and leave the antinics on for a couple of hours before I turn out the lights for the night. They don't do it all the time, it is sporatic.
125 Gal-35 Gal Wet/Dry-Tetra-Tec PF500 HOB
(3) AuquaClear 301 Powerheads-600 GPH
Automatic Tempature Controller
5-6 Inch Sand Bed-200+ lbs of LR