I recently purchased and currently housing a ball in a 20G glass vivarium. As of now, I am using two UTHs with a cheap rheostat. It was less than ideal so I bought a couple of thermostats that arrived today. I plan on modifying the cage this weekend. My question involves the placement of the thermostat probes. I have been using this guide for setting up the vivarium:

http://ball-pythons.net/forums/showt...ass-tank-setup

According to the guide, the probes should be placed on top of the repticarpet, under the substrate. However, while researching thermostats on this forum, I noticed several people stating that the probe should be placed between the heater and the glass (outside the tank). I would think that if you put the probe between the heat pad and the tank that there would be a few degree difference between the temperature there and at the top of the substrate. Looking for suggestions on which is the preferable placement. The thermostat is a herpstat and I am using a bark substrate on top of repticarpet. Thanks for your insight.