32w on 10g too much?

I have 32w CF over an (odd size) 10 gallon tank. The light is about 2" from top of tank. I'm thinking this is way too much light for a "low light" setup.

Tank Size: 18w x 11d x 12h
Light: Current Satellite SunPaq (20") (normally 40w CF, but I have a 32w in there).

The biggest question is: Can I stick an 18w CF bulb in there? When I looked at the ballast, it had 40w/32w on the sticker. I like the look of the fixture, and I have not found a T8 fixture that can go over open water (which I think would be ideal). I'd prefer to go the Aquasoil / light water column dosing method (which will involve replacing the substrate, ie tank rebuild)

Currently, I am dosing Excel, and have slow, but steady algae growth. Light is on 6 hours/day. Moderate planting, high flow via Rio 50 powerhead (but will need to slow it down when I go to low light...am going to get community female bettas)