Co2

over the course of 3-4 months you need something like 30lbs of sugar and approprate ratio of yeast even for a small area ( volume is better word). this is something you can reference with a google search.. the molar ratio of this chemical equation will be incredibly accurate and precise for such a guesstimate. (i.e. you can trust the math) 1200-1300ppm is the goal. if you do this in earnest get a co2 alarm or something... don't die due to stupidity and laziness. That would be the definition of "natural selection" at work. so i'd wager 1/4 to 1/2 lbs per day... could opt to use it only in flower then it's just 8-10 weeks of sugar instead of 12-14 or more. again how much sugar and yeast ratio is a simple google search. don't rely on what someone repeats.. make sure whatever you reference is using the chemical formula for what is occurring... the molar ratios are true and consistent.

Unless your grow room is sealed up and recycling the air not venting outdoors its wasted money, I agree you should focus on the basics and ignore the CO2 for now. Indoor air like in your apartment/house tends to be higher in CO2 then outdoor growing so that should be fine for now. A big part of how well a plant grows is in its genetics. I'm growing 6 plants all the same stuff and one of them is much denser nugs vs the others, not from CO2 but just how it grows. If you get there one day in a sealed room and want to use CO2 I would look into buying compressed gas cylinder, its better in the end and more stable/easier to control. If you want a more natural route they have a bag of fungus "mushrooms" that create CO2 n good amounts. Think they are called exhale bags I think. Dry ice can also be used if you have access to it. but in the end I think the cheapest option is compress gas just has a higher footprint setting it up like most things in Cannabis industry. If you set on the yeast thing keep mixing in more sugar and water to keep the reaction going. Change it out every now and then as the amount of alcohol in it will affect how well it is reacting. Start with less yeast and it will build up slower and last longer. start with more yeast and it will be faster and not last as long. Good Luck!

I would just focus on the basics. Yes technically CO2 can boost growth but it has to be applied properly, in a suitably sealed environment, at proper concentrations in the appropriate time of light cycle to be beneficial. Reaching a meaningful level of CO2 concentration via fermentation is gonna take a lot more than you think....like a brewer bucket size(6 gal) container at least and controlling output is impossible. Serious CO2 growers tend to use dry ice or tanks and commercial guys use CO2 generators that burn propane or natural gas, it's more practical. Again though, it's a waste if done improperly.

Don't bother with additional CO₂ Unless you are an experimented grower who already have optimal environmental variables and want to push yours plants over the Max point (in that case, sorry I don't known any recipe), CO₂ don't make your yield much bigger.

1 cup of sugar, 1/2 tsp yeast, and 1.5 liters of water. It would last for around 2 weeks. From what I understand if you use champagne or brewers yeast it will last substantially longer. I think the premise is that alcohol is a by-product of the fermentation process.