I bought a maxima clam over the weekend that's about 2 inches long. I placed it on the rocks in the middle of my tank on what I thought was a secure surface and twice now he's scooted off the rock and onto the sand bed. Should I just leave it in the sand? It looks perfectly happy there. I have 2 250 watt MH and 4 56 watt T-5's about 30 inches above the sand bed.