Your plants need co2 yes, but you need to ventilate to keep fresh co2 coming IN to your environment. Plants will absorb the co2 and convert to oxygen. If you dont have any fresh co2 coming in, you limit the amount they have access to.

Ventilate as it keeps fresh in and by product out. It simulates outdoors very much which is the way nature designed it.
HARDDON Reviewed by HARDDON on . Ventilation! Why do i need it? Okay so plants breath co2, right? If my plants are in an enclosed area, with co2 filling the area. And Carbon Dioxide is heaver than Oxygen, than I can keep an all co2 environment, I mean as long as you have an open top for the O to get out. Or am i totally out of it! Rating: 5