seriuosly. I have never used one. I have always just stuck my hand in there and got use to temps by feel. this is the way to go. Once you get use to it you will never need the thermometer again. and to my experience where I fish (could be different where you are), in northern florida, the fish need a big difference in temp to change their pattern. but the good thing about florida is it never gets freezing cold. so if you live north of me then forget everything i just said. LOL