Sorry to jump in the middle of this, but I agree with Kara that for herps you should have a temp gun. The main reason is that surface temps and ambient temps are two completely different things. What if you are in a room with ambient temps the in low 70's, and you are setting your heat strips to maintain ambient temps of 92 high and 82 cool. Well you are probably pushing suface temps above 100 to heat the air space in the tub. One of the features of most temp guns is a scan that lets you cover the entire surface of your tub and will report the highest temp, its a great way to check for "hot" spots. On the other hand if you are just doing surface checks with a temp gun (or your thermostat probe), you may be running ambient temps too low.

Neil
(And not the one Kara is referring to)