I have a new tropical terrarium of a few weeks old. It is a 20 gal aquarium,2 15w CF and one 20 watt flurescent tube,
a variable speed fan,good drainage with lots of tree fern fiber in the substrate, and a glass lid. I have experimented with changing the lid opening, fan speeds, water sitting in the pebble layer of the tank and misting. I just cant seem to keep the humidity any higher than 65%. It averages around 50%. I mist once or twice a day and the fan dries off the plants nicely but the humidity will only remain at 69% temporarilly. I do get 1/4" water remaining in the pebble layer after the misting drains. Now that the cooler temperatures of fall are here I try to keep the top closed most of the time with no change in humidity. The temperature from the lights remains 80-83 degrees from the lights. I do live in dry AZ but I have a 10gal terrarium with the top open half way and the humidity is 73% without misting but the substrate has more coco fiber in it. Maybe my substrate isnt wet enough to keep up the humidity ? but the soil just stay consistently moist, not wet which is perfect.