There's a lot of T5 setups out there. Your 75 is about 20" deep, minus the sandbed, so a 6 or 8 tube fixture with individual reflectors would be a good choice. Of course, you'll want to eventually customize your tube choice, the tubes supplied with the fixture will be a middle-of-the-road selection. There's a bunch of T5 info out there, delving into tube preference, color rendition and coral growth, etc.