I don't get it, Do you?

[super7]

I have a 150w metal halide and 100w of VHO. This lighting is on a 24" tall tank. I will be upgrading but something is wrong. My SPS is bleaching when up high near the light(about 6 inches under the surface) but when moved down they start growing again and have full polyp extension.

The water chem is

phosphate 0
nitrite-0
ammonia- is 0
nitrate-pretty much 0
pH is at 8.4
salinity is at 1.025

If you have any ideas on what is going on, please reply.
Thanks Super7