Get rid of the undertank heater. They really are useless with dragons can pose a serious health hazard for him. The pet store ones can short out and cook your dragon or worse, cause a house fire.
Use a regular household bulb and hooded fixture you can get a home hardware or home depot or any similar store. Set this up over your dragon's basking spot and with a digital thermometer with probe, adjust the bulb size or height of the light so the basking temperature is between 95-110 F.
Nighttime temperatures between 65-70 F is alright. If it tends to get colder than this at night, a lightless heat bulb can be used. (either blue bulb, or ceramic heater bulb). Don't leave teh UVB light (or the regular household bulb) on 24 hours as this will cause stress and other problems for your dragon, as was already mentioned. Best to set them on a timer, leaving between 10-14 hours of daylight (or just match the length of day to your area, so less daylight in winter, more in summer).