I don't know where you're looking to get extra CO2 from, all I know is that it can help, when you've sort of hit maximum performance and have really good/strong light.....
So how much variance can there be in CO2 levels? I would think it's fairly in line with the outdoors/atmosphere CO2? Unless there's a bunch of people in a smaller enclosed space? Or worse, some sort of exhaust leaking in......but if there are meaningful fluctuations that's a new one to me. And if that is the case, then something to move the air would be in order......then I don't know how much extra CO2 is needed to make meaningful improvements on plant growth. If a small sealed bedroom that a couple is sleeping in shows 5% more CO2 in the morning than when they went to bed, ok.....but if that's nowhere near what plants would need to show measurable improvement, there goes that. Exhaust would start getting dangerous, and even if it's going to be actual tanks of controlled release CO2......then there's the hassle of dealing with the tanks in and out, getting them refilled, etc.
So that, and.......back to your harvest. ;) . I want to harvest, but these cotelydonallies don't have much resin. :(