I just got back from Home Depot. I got a ballast the holds 2 bulbs. It cost $16.99. I also got two 6500K bulbs to put in it. I couldn't believe how much of a differenct it made in the tank. I also kept the old ballast with the one 40 watt bulb. I just moved it to where you open and close the lid. When I actually have to open it like to feed the fish, I can just put it on top of the new ballast. I can't believe how much of a difference it made. Thinking about it, it was a pretty big jump, going from 40 watts to 120. I hope the plants will do a bit better. They started to look a little brown, but I think that will greatly change.