i got my atlantic reef octo about a week and a half ago. hes eating well and moves alot if we pick up a rock to get an empty snail shell or something, but lately he has been staying in a little hole in a peice of live rock and he keeps an empty snail shell with him. is this normal? he's about 6" from tentacle to tentacle (wingspan?) and his head is about the size of.. a ping pong ball. thanks!