I finally bit the budget and got a metal halide fixture! ;D My fixture has 2 250 watt MH and 4 96 watt actinic lights. I have a dersa and a crocea clam. I am pretty sure it is a crocea clam. Can I put the rock that the crocea is on - on the sand? or does it need to be closer to the top? It is on the sand now, but under the MH. As for the dersa, its on a flat rock that I buried in the sand so that it looks like it is on the sand and it too is under the MH. Am I doing it right?