The water will try to equillibrate itself with the atmosphere. Hence only water movement will do the trick. What we do is force CO2 into the water making higher CO2 there rather in the air so the plants can do luxury uptake. We do this with concentrated CO2.
If you have really low light, then you hinder the photosynthesis process and the plants wouldnt demand so much CO2. Then it would work.. All is depending on what type of aquarium you want. High or lowtech.