no CO2 my exhaust fan clears the air too fast for CO2 to matter, its just that I live in Az and dont have AC in my place atm lol, there have been days where it has gotten to 100 in the box for an hour or two before I could get it back down, but due to the DWC and water temps in the 70's they can handle the heat waves, it gets dangerous for seedlings sometimes but once they have decent roots they do fine. cannabis is an amazing plant and can handle very high temps as long as they have plenty to drink, they can also survive a lot on the other end of the spectrum of temp as well as my outdoor grow was planted early this year and got hit by a cold snap with temps into the high 20's at night for a couple days and they all survived that as well.