My guess is he isn't eating because it's getting too cool. Mine starts to lose interest in food and try and aestivate if it gets below 75 much at all. If it's going down to 70 at night, that's probably why he's not eating.
What sort of heating equipment are you using? Even if you don't turn the heat up during the day (which you probably could... adults can handle daytime temps in the 80-85 range) you could at least turn it up at night.