there is a 180 teardown thread in the selling forum, maybe pick their brain and look at their equipment. i know nothing about lighting for tanks that size though.
But they do make 60" T5 bulbs. I ran several 60" T5 retro kits staggered on my 180. Worked out well. That way you only have to buy so mnay bulbs.As far as t-5's, they don't make 72" t-5's, which means I'd have to have two sets of 36" bulbs, and when you talk about buying between 14-16 of them at $25 bucks a piece each year that adds up!