Fenton to answer your question about the temp difference being because of the thermometer location, yes it can make a difference, but it shouldnt make that big of a difference. you should be able to detect a temp difference that large with your bear hand. As aldiaz suggested, get an in tank thermo (i just bought a cheap one for $3) and check around the tank for temp changes. It could very well be a problem with the thermometer too so getting an in tank thermo could rule that error out
