From what I have read I am thinking lack of light. The corals went brown, but had huge PE possible trying to get more light, plus you had the acros mid-bottom?
I don't know on the monti, it should have been fine but the acros sound like they could have been shadowed out.
If the tank is more than 18 inches deep I doubt the MH was even really reaching. If the tank is 24 inches deep 250W MH would be the tiket, if it is 24 inches + deep then look into 400.
But before you get any lighting upgrades try the acros right under the bulb, that may help, and make sure you get frags from other peoples tanks, not wild cought colonies. Frags are easyer to keep.
What are the dimentions (in inches) of your tank?
HTH,
Whiskey