40-50% humidity is ideal for flowering. There is a trick if your able to control humidity, is to drop the humidity below 40% the last 2 weeks of flower. This increases trichome production. I cant wait till i have the proper setup, so I can do this. Added co2 is really only needed for growers with high wattage HPS lights. I see so many growers using all these products to add extra c02, but it is just a waste.