air exchange in terrarium

[travelfin]

Anybody have facts on how much should the air change per hour. To my knowledge the air in a building changes once per two hours. Greenhouses run between once an hour to once per minute. If the air doesn't change how long does co2 last for the plants.
It is easy to have high humidity if the air changes slowly and very difficult if it changes fast.
Searched the net for an answer but found nearly nothing. Only for greenhouses.
Which is better slow change and high humidity 90%
or fast change and 70% humidity.