Every day, between oh, say 9:30 and around 10:30 my xenia contracts incredibly tight. At first I thought maybe a crab brushed against it or something... but After a week of noticing htis behavior every night (my wife watches while I am at work for me) I have my curiosity up. The coral seems healthy, it along with the colt and star polyps have increased their size exponentially.

Is this common? is it an indicator of something?

I have my lights on a ~12 hour photo-period, on at 10:30 AM, off at around 10:45 or so I think (they are on a timer, but not exactly 12 hours)