Steve, hex tanks are hard to light for reef. For fish you can go with standard flourescents. If you want to keep corals a single metal halide pendant would work well just have to raise it up a bit so it doesn't warp/bow the acrylic. I have a 20 hex that my mantis lives in currently and I'd love to put a better light on it and find some corals to keep in there.

You might be able to build a small overflow for the tank but not sure how well it would work on a tank that's tall like that.