I got a new crocea clam which I think is very happy in my tank. I have 2 175 watt halides which are mounted 12 inches above the water. My tank is 20 inches deep. It is on the sand right now, but dont croceas like to be on the rock? I have a sand bed with a plenum underneath, and I do not want him to bore into my plenum. Should I move him to the rock? 8O