Sorry bout the double post but I cant seem to get into the post edit. Just to make it clear the coolest portion of the tank will most likely register on the surface whatever the ambient temp is, maybe a wee bit higher. So iif your ambient temp is 80, the surface all the way on the cool side will probably be right around 80, therefore the center of the tank (surface) will be maybe 85, and your hot spot 90 (just as an example)