i can promise there will be a couple peopel who will swear you have to have mh
to have the best looking coral and the healthiest coral. not true
its personal prefrence i think. im putting together a 75g also and am going with 6x54 t5. it was a hard choice thou. with mh
you have a shimmer effect with the water that almost everyone likes. but you have alot more heat and less bulb option/combos then what you have with t5.
with t5 you have no shimmer effect( can be added with some led
's) and less heat. you also have the ability to add diffrent bulb combos. you can add the 10k bulb for growth, the 20k bulb for color, the antic for color, the possiblitys are endless especially with an 8 bulb combo. also what i like about t5 is you have the same wattage coverage over the whole tank. what i mean by that is if you have 300 watts on the left side with 2 10k , 2 20k, 2 antics, a fugi purple and a blue plus on the left side you will have the same thing in the center and the right side. with mh
you have one bulb covering 2 foot of your tank and if you use diffrent bulbs on each mh
. it doesnt translate to the whole tank. only to that one 2 foot section.