well, this is not my section but what research I have done, you won't need a cO2 system to support a few plants. 40 watts sounds a bit low, it is my understanding that with exception to atinic bulbs you would idealy want to have power compacts like that used in marine tanks. I have been trying to find out why fresh plant keepers dont like atinics, my salt plants do quite well with them, but have not yet gotten an answer.