The heater I'm talking about is the Hydor Mini Heater:
http://www.aquariumguys.com/miniheater.html
You can get them at Petc0 for sure, but support your LFS if they have 'em
It's a little paddle with a suction cup. You could bury it under the gravel and just run the cord out of the back. I'd pick up a thermometer too, just to keep an eye on the temp. You don't have to leave it in 24/7, but pop it in now and then to make sure it's the right temperature.
Also, make sure you have at least 1 thing that the fish can hide behind. A silk plant would work just fine.
__________________
current setup:
5.5 gallon low-light planted tank
-1 dwarf puffer named Beep.
for reference: my name is Julie
