Just so everyone knows it is normal for he surface to dry some. If it never did then there would not be any humidity without misting. Moisture evaporates from the soil no matter what heat source is used. There is always a drying effect. Makes the substrate a little more moist and some of this probkem will go away for a while. Allow it to be moist enough so that when squeazed it will drip some. This will help keep the soil more moist longer.