Mephisto Blue Toof Attempt 2

If the air where you live is naturally dry, there's very little you can do, unless you do a closed room grow. Low humidity won't be a problem, so I would worry about the temperatures first, although 81°F is nothing to worry about; but if you want to lower them, go ahead with the AC. Second, as the plants grow and their water intake grows, the water they transpire will increase and so will the humidity of the tent.