A 250 DE would be perfect for clams on the sandbed and any sps....and the new 400 DE's are coming out but there way new, I suspect that they may be for deep tanks, like 30 to 36inches in depth, but there still new, so the jury is still out on that one, but go with a 250 DE...I like white light and more PAR so i go with 10ks, if you like the blue look, go with a higher kelvin rated bulb like the 13k or 15 k or 20 k bulbs.......