What kind of thermometer were you using to measure temp/where were you measuring it at? The cageside thermometers they sell at Petsmart are really inaccurate and in my experience tend to measure higher than the actual temp. Unless you have a spaceheater or something in the room, my guess is that it was actually cooler in most parts of the tank than it was reading; I've never been able to get tropical temps right with just a heatpad.

Also, what type water were you using to expand the cocofiber? I've got a WTF as well, but he spends so little time actually on the ground that it probably wouldn't even phase him if we used pool water to expand his bedding. Since pacs burrow they're a lot more sensitive to whatever you use on the substrate.