co2 can be added anytime some wait till its flowering. What kind of ventilation do you have is there a lot of fresh air in your space?
How many plants are you going to grow?A fair bit...lots of cool and a fan.
co2 augmentation IS NOT NECESSARY, but co2 IS NEEDED TO GROW ANY AND ALL PLANTS(that i know of). so as long as you have like 150+ ppms of co2 present in your space then plants will grow. but aprox 1500ppms is the optimal amount of co2 in your air.I have never grown before (yet) , but i do remember seeing a high times growing video on youtube saying that CO2 is not nesseccary for marijuana. was this false information?