tank lighting

[jntmcduffie]

I am trying to get some help for my 55 gal coral tank...i have someone who will trade me some MH lighting but the problem is that the unit is too tall for my canopy it will stick up about 3" higher than my top. the unit has 2 175w MH lights and 2 Antionic lights (not good speller). the unit has remote ballist and 2-4" fans. How high do the bulbs have to be off the water so i will not have a heat problem. My canopy is only 6 3/4 inches from the top of the tank...can anyone give me some advice?

Thanks
John:unsure: