Co2 humidity & temp

Well I got my temp up and humidity with room humidifier. As far as co2 when does it become more nessasary to my grow I have fresh air vents open so I know they getting some. And how much water and how often they are a week old.

Unless your adding co2 and you have open air flaps you got nothing to worry about with co2

Air exchange is one factor, enough light is another.