Humidity Dropping Way Low

You must have a basic AC Infinity. See if you can add the digital controller to your fan. This allows you to program the humidity and temperature you want. Then the fan will turn on and off as needed to maintain the parameters you set. With four fabric pots in the tent your pots should be evaporating almost all the moisture you need once you stop running the fan continuously. Even though your plants might not have roots to the edge of the pots, thorough watering the edges will create a natural moisture reserve that evaporates over the next day humidifying the air. --- I use 3:1 Ocean Forest and pearlite in my grows and it has worked great. I started with Happy Frog but get better results with Ocean Forest. And, do not add peat moss. It's already in your potting soil so why add more. Pearlite has the benefit of improving drainage and aeration. Couple that with fabric pots and you can gain some of the benefits of hydro with the ease of soil growing.