The LED fixture is a recent addition so I forgot about that part of the 'tech'. It had a 24" 65W CFL on it before, no CO2, some dry ferts when I remember.
The fixture has 14 3W CREE LEDs and is dimmable, that's what I was referring to as lowest setting. I acquired the fixture from a local member and fixed it up a little bit. I have a short thread in the DIY section about it.