Hold on here folks.. I seem quite the over simplification of co2 use going on. Temps of 90 neccessary? Ummm no.
While it is true that higher temps boost a plants metabolic rate which enables then to take advantage of higher co2 concentratuins, advising a somewhat newb to set it and forget it at 90 is, well, it's just not good advice.
Optimum conditions change throughout the growth cycle and day time temps are just one of the factors, nighttime temps and more importantly, the difference between the two is equally important. If your room is at 90 then your plant tissue is likely at 95. It's just too hot.
Those temps are good for veg and maybe the first two weeks of flower but unless your having hotter nights, your going to get some major stretch going on.
I'm not going to sPell out the ideal situations for all phases.. I mean, it took me YEARS of research, trial and error. And then inevitably some jack hole will just say nuh uh. But needless to say as flowering goes on, your temps and co2 lower. We are at 77 and 800 during the bulk up phase and 74 and 600 during maturity.
You could run 90 degrees all day long and nothing bad is going to happen, but in terms of bud quality...nothing good is going to happen either.
Peace