Are you still using a heat bulb? They dry the air out immensely and I found it impossible to keep proper humidity in a glass tank with a light. I switched to a ceramic heat emitter bulb and UTH, both on separate thermostats and between that and a damp towel on top I can keep my humidity around 60% all the time re-wetting the towel maybe once a day.. This is in my house where the average humidity is around 40%.