Basically..... veeeeery basically, when the probe is on it chills the ceramic shaft. It gets pretty darn cold. I have a temperature controller so it will only turn on when the tank temp goes too high. It won't work very well on a tank that needs to drop a lot of degrees or one that is very big. This is about the max IME.
Going to get hanger wire for the fixture tonight as well as a grommet. Then it's off to the pier to buy my fishies some fresh food.