Lighting Issues with Corals

[LeanneP]

I have been having on going problems with my lighting. I have a 90 gallon with 2x 250 watt MH lights. For months I have been using screens to cut the light back and every time I think that I am finally getting somewhere the corals look terrible the day after when the halides come on again. I was down to one screen on each side yesterday and now my frogspawn and hammer corals are closed up as soon as the lights come on and I have put more screens on again. My parameters are all good so why is this continuing to happen? I also had 2 colt corals that disintegrated at different times over the past month or so. I keep thinking there is something wrong with my tank but I am at a loss as to what. Any ideas?

Leanne