Sorry I think I'm not getting what your saying.
If I used less Co2 I would have to cut the light because I would be Co2 deficient.
I believe I have (up until the air stone) a severe o2 deficiency.
(due to glass and canopy)
I think both you and daniel just said the same thing haha. You are correct that light drives the CO2 demand by plants. I would advise against the airstone during the day since you will be degassing CO2 quite a bit. What you can do if you don't have a wet/dry filter is to increase surface agitation or decrease your light as you said. This can be done by a small fan, raising filter output, powerhead pointed up. Just try not to break the waters surface too much.