I can't tell you for sure that it will or will not work. I would be worried about a clam on the sand. Put it in the rock, higher up in the tank and I think it would be fine. My clam is on the sand, 21" below a 150w MH
and it is happy as a clam (growing), I really do wish that I had gone for the 250w fixture though. This is my 3rd fixture! Next time I upgrade it will be to 400w.
My coraline did bleach but then came back. It still grows on everything, though coraline is a low light algae.
I'm thinking of turning my 30 gal
QT into a frag tank and I wll probably go with a T5 fixture over that instead of a single 150w MH