Got this guy on Saturday. I acclimated him for about 3 hours and then put him in the tank. He went directly to the bottom by some live rock, and then found a little cave under the rock. He's been there ever since. I can see him when I shine a flashlight in there. Sometimes I see his head. Other times I see his tail. How long should I wait until I start to worry? Nobody in the tank even had a chance to bother him. So, what's the deal?