I currently am running 2 - 48" T8NO 6500K flourescent tubes for 10 hours a day and run 4 48" T8NO tubes for about 6 hours a day (the fixture sits directly on top of the aquarium), which I imagine would put me in the low - medium light range.
My problem with DIY CO2 is getting "enough" CO2 into the tank. Perhaps its just me, but it doesnt seem as though the DIY systems are effective at delivering an ample dose to a tank of that size.
* To clarify the above, I have a four light system. I run 2 bulbs for 10 hours, and then within that 10 hour window I flip on the additional 2 bulbs for about 6 hours.
My apologies to the OP, I wasn't trying to hijack your thread, just made me think of my own tank when I read your comments.