Temps before humidity NEVER sacrifice temps to get humidity! That said there are a handful of points here. The first is humidity rises the open top of the tank is where humid air is lost (heat too). Tanks oddly do not vent as well as most think so I am not a big fan in blocking off air flow. I usually suggest leaving the top open or using a side turned tank.

http://ball-pythons.net/forums/showt...arium-Solution

Not always practical. The way I increased the humidity in tanks was fairly simple. I use coco coir I am not sure if it would work with other substrates. I banked the substrate so it is very thick (deep) on the cool side and thin on the warm side. Under the cool side I placed a plant drip tray. This is completely under the substrate. I would poke my finger down to the tray though the substrate. Fill the tray with water via the hole I made and then fill in the hole. The tray allows the under layers of substrate to become wet while the surface stays dry. The water vapour rises and humidifies the tank. This kept 55-60%rh in the tank while it was located in a room that runs in the 30s. I would fill the saucer every 5-10 days depending on the RH in the room.

The second issue is digital hygrometers come it two flavours... expensive and accurate (fragile too) and cheap with suspect accuracy. The good ones simply are too expensive to be useful. Digital units are effected by damage to the cords, battery life, dirt, liquids, manufacturing issues, and just plain design. It is also quite likely that many digital units are just not reading correctly. (accurite in the last specs I saw stated that the unit read in a 30%rh window of accuracy, 15% high or 15% low and still be acceptable) Analogue units are less sensitive to dirt liquids and junk they can be very robust they do need two features to be trustworthy. A METAL face card. (Cardboard warps and interferes with the needle movements) and a calibration screw (usually on the back) this allows the unit to be tested (salt test) and corrected if found incorrect. they in my experience (I own 20 or so) hold in 4% rh and often with in 1% rh the limit of a salt tests accuracy.

i like the western instruments certified hygrometers myself I found they come correct and hold a high level of accuracy for extended periods.

http://www.amazon.ca/Brass-Analog-Hy...pd_sim_sbs_k_1