74-78.6f is the optimal range for cannabis...temps higher than 79 will force the plant to close stomata and focus energy to plant processes other than bud production.......
CO2 used at appropriate levels will keep stomata open allowing plants to "breathe" at higher temps and, according to many growers produce more abundantly....
I don't use CO2 at this time as temperature control is not an issue for me.....it will be added down the road in order to increase yield once all other conditions have been perfected. I don't consider it necessary unless it is impossible to maintain the optimal temperature range.
