The tank is about 140 gallons. Clearance in between the two plant media containers is a bit too little, it's only just over 10 in.
Kind of an architectural sacrifice there...
I'll look into those lights, thanks.
the male Tilapias are close to a foot now.
What are the dimensions of the tank and how many fish?
Ya, 10" is rough. It looks great though! I find that you want to give yourself about 18" between the top of the substrate and the light, otherwise you will be constantly trimming. More for crops taller than lettuce and less shade tolerance, but then you are getting into multibulb fixtures and pushing the limits of flourescents. It sucks, but the best info on indoor gardening with lights comes from the pot growers forum. For taller plants, like tomatoes, you could do vertical flourescents and a cfl at the top, or go hid. Flouros are best watt per watt but lack the penetrating power of hid, and so are not always good for tall light loving plants unless you don't mind a less productive understory.
If you want to flower in the off season you will almost certainly need an enclosed cabinet, which is probably the most efficient for indoor grows regardless of your goals.
If I remember, tomorrow I will post some links that show good vertical systems that get around the height limitations, but you still can't expect to gain much in terms of output per footprint without going very tall. The trick with hydro is that it does let you place things closer together due to less extensive root system, but the leaves still need light. Think of leaf lettuce kind of like crypts, plant them with some space and the leaves fall open in even layers, but plant them close and the leaves stand up, butting against eachother and forming a tight rosette.