He's a cutie! You mentioned using an UTH and thermometers. Are you using a Lamp Dimmer or a Thermostat to control it? If not, UTH's can reach up to 130*, and that could've been what caused it.
Edit: This is a thermostat that is cheap. Of course, the more expensive ones are typically more recommended. I use two of the 500R's and they work fine.
This is a lamp dimmer that I personally use, also. It's good. Does the job!