C02 is best taken in by plants when the plants are usually at the higher temperatures now yes they do need it and it can improve growth but indoor places such as houses and apartments usually have a gas boiler with a pilot light that alone is enough for the plants to take up. If your talking about enriching your nutrient solution with co2 I think this would probably a bit too much but that's just my opinion other growers may know more about this but being a dwc grower i have never added co2 to my buckets and they turn out okay :)