Try and warm up the tank to 78'F during the day and 76'F at night. You can add a UTH (under tank heater) pad to one side. Temps too cold will slow down their metabolism, make them less hungry, and can actually stress them. This makes them more prone to illness. Is it possible to turn up the room heat a bit? I used to use a ceramic heat bulb in a dimmer dome lamp. It worked nicely but it can really heat the top screen, which I did not like. I now heat the room with a ceramic tower heater on a thermostat, though I doubt most people would want to do this. I have 14 frogs in my room and a gecko, so it's much easier than a bunch of heat lamps. You can also use a 50watt red heat bulb in a dimmer dome lamp. The heat level can be adjusted by the dimmer switch on the cord to the heat level you need. The downside with heat lamps is they dry out the tank, requiring more mistings, and if you're not careful and you mist the bulb or hot glass with cool water they can shatter. Some turtle bulbs have a safety coating on the glass of the bulb to prevent this. I use them for my turtles. The UTH heat pads are easiest. They will raise the temp anywhere from about 2 to 5'F estimated, depending on the size pad you get.