Many of groupers are usually inactive during the day, but this depends upon species, too. I know some groupers like to swim out in the open. I used to have a V-tail grouper. I eventually had to get rid of him because of his cantankerous temper. Anyway, he usually hid in the cave all day except when there was any food present. An interesting thing about him is he could change his body color/pattern like a chameleon, which ranged from almost white to intense red......That was one fish with an appetite that could not be matched by any fish that I had.