An aquarium thermometer is a device used to measure the temperature of an enclosure that is used to keep aquatic organisms. There are many kinds of aquatic plants and animals that can only survive in a specific temperature range. People who want to keep such organisms in their homes or in a setting that allows for public viewing typically must maintain this specific temperature range to keep them alive. Various heating and cooling devices are used to maintain the water temperature. An aquarium thermometer is used to ensure these devices do, indeed, keep the water at the correct temperature.
An aquarium thermometer can come in several different forms, though most are composed of two primary parts: the temperature sensor and a means to express temperature in a meaningful manner. The sensor is the part of the thermometer that reacts in some way to changes in temperature. The other main part of the aquarium thermometer must be able to express the sensor's reaction in a way that can be easily read. The end result is that one is able to see a relatively accurate temperature value. Additionally, an aquarium thermometer generally must be waterproof, as it will generally be underwater.
Digital thermometers, mercury thermometers, and other forms of thermometers can all be used in aquariums. A mercury aquarium thermometer or similar form of non-digital thermometer can often be attached to the inside of an aquarium with a suction cup. Sometimes, such thermometers are simply allowed to float on the surface of the aquarium. Digital thermometers, on the other hand, often feature a display and a sensor separated by a relatively long cord. The sensor is placed in the water while the display is kept outside of the water; this prevents the display from suffering water damage and makes it easier to read.
Thermometers are generally considered an essential aspect of any temperature-sensitive aquarium setup. Aquarium heaters and coolers are typically able to maintain the correct temperatures, but malfunctions, power outages, and fluctuations in environmental temperature can alter the aquarium temperature. The presence of an aquarium thermometer allows the individual who takes care of the aquarium to respond to problematic changes in temperature. In some cases, the thermometer can be equipped with an alarm that sounds when the temperature drops to dangerously low levels. The proper use of an aquarium thermometer can prevent aquatic plants and animals from being harmed by their environmental conditions.