halide upgrade-need help!

[bv_reefer]

well i currently have a great oppurtunity to upgrade my lighting from 2x70-watt hqi's, to a 1x400-watt. Again this is for my 33-gallon. I'm really nervous about it because it's a jump from 4.2watts/g to 12.12watts/g. But the absolute last thing i need is all my soft corals and lps bleaching from it, what can i do to avoid bleaching or shock. where and how high should the bulb be from the surface of my water, my current bulbs are about 5'' from the water surface. any suggestions greatly appreciated-