Great tank, I had a very similar setup and plants in a 115 tall(
http://www.glasscages.com/?sAction=OrderForm&sProdID=AQ_11548 x 18 x 31). Plain sand and gravel, 2.5-3 watts of CF lighting, minimal fertz and my plants basically flourished on healthy load of poop from my rainbows and tetras, and water changes alone. Yours is another testement to the minimalist approach that you dont need fancy/expensive equipment to have a successful planted tank.
I think in my next tank when i return to the US I may go with a 125 or 150 in a longer and shorter version. While it looked great, the maintenence standing on a chair and reaching down into the 31 inch tank was a pain. I also felt my lighting was the minimum the plants could stand, especially in the tall tank
I wonder if I might not go with some simmilar lighting approach to yours instead of the expensive compact flouresents.
Using the bulbs you do, how long do you keep them turned on during the daylight period? How often do you replace the bulbs and do you replce them regularly or only after they burn out.
Is the tank getting any natural lighting?
Do you have moonlighting?
And finally would you link me to or snap me a picture of your fixtures and lighting setup?
Thanks, and again nice setup.