Did you buy the fixture yet?
I am not going to use a MH lamp for a few reasons. Here's my logic...
A friend in our local aquarium club is using T5 bulbs instead of MH. As a result, he spends less on power, doesn't have to worry about cooling his tank, invested way less in his equipment, and doesn't have to worry about evaporation-caused salinity swings.
But, if you really are thinking about a MH system, I can get you a good one, cheap, through another friend. I will PM you the deets.