Been there myself.... LOL
Some corals will definately react adversely but most (button?) polyp corals are fairly hardy and should survive just fine. It really boils down to your water quality and the diffference in chem between your tank and the tank it came from.
Chances are it will just take longer to acclimate properly and fully open. Keep tabs on it for necrosis but other than that there not much you can do. With MH
lights, I would also suggest placing it low in the tank at least for the time being. Although 2x175 on a 90 is not overly intense, all the extra acclimation TLC you can give it the better.