If you go to one of the big box stores, and go to the electrical supply area, you can get galvanized conduit piping really cheap. For whatever reason, the HD's in my area are a LOT more helpful with stuff like bending a length of pipe or cutting a piece of molding. You can make L brackets that you can suspend over the top of the tank by drilling holes in the conduit and attaching it to the back of a stand, table, or whatever the tank is sitting on and suspend the light fixture/s from the ends of the "L's" as your settup dictates.
If you don't like the look if silver conduit, you can slide black vynil hose over it.
I made an LED pendant for my hex that cost all of $40, and that included $23 for the 5500K LED spotlight.