Swimming Thermometer Types：
They’re relatively simple tools, but pool thermometers have more features than you may be aware of. They fall into one or more of four basic categories: mercury, digital, floating, and handheld.
A thermometer can be either digital or mercury, and be of the floating variety, but handheld thermometers will, of course, always be digital.
Mercury-filled floating thermometers can be damaged by severe weather and overzealous swimmers. If they break, you could have a real mess on your hands, including mercury in the water. Not to mention, broken glass could rip your liner, or worse, hurt a swimmer.
For these reasons, we highly recommend using a plastic, digital, or handheld pool thermometer.