I would go with a two bulb T8 fixture. Unless you're going to do CO2 those T5's are going to be too strong.
It's a pretty deep tank though...? Definitely don't plan on using CO2...! It's 18"s deep, and has a screen hood, was originally for a reptile. Probably just going to hang the fixture above the tank, but if I go with a T8 setup should I go with something like this...?
It's cheap, and holds two T8's...!