My suggestion would be to buy a Heat Gun. There is a banner on this site for one that is $50. It's an awsome thermometer, it really has helped me allot in getting accurate tempatures. I can get accurate readings of the surface temp whenever I want instead of having to put the thermometer in the tank and then waiting 24 hours to get accurate readings.
If you don't want to spend $50, try Walmart, I saw a few in their Hardware section of the store when I was looking for a Thermometer / Hydrometer.