Stewie's Ok! i took him in to the vet and he said my problem was I wasn't keeping the pen hot enough at night. I got a bigger night light but the pen is so long that it is still too cold in the middle and cold end of the pen. i switched him to carpet( the vets xray found sand in his stomach). would an undertank heater placed in the middle of his pen be too much? i have the same problem at night, still a little cold.
by the way, stewie( my dragon) looks a lot better and is eating like he was before, all overnight.

An undertank heater would be fine if there was a thermostat to regulate the temp. of the pad so that it doesn't get too hot.

Glad to hear he's ok!
The best way to make sure that your temps are ok is to use a digital thermometer with a minimum/ maximum function. It will tell you how exactly what the temperature range has been. It may surprise you what happens in 24 hours. They have a remote sensor that you can move around the tank to check out every section. Walmart has them for about 10 bucks.

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Merlin,
What's Life Without A Little Magic!

i put an undertank heater on a thermostat and it seems to be working great. i think i'll invest in a digital thermometer tommorrow. thanks for all the help!