Aquarium Thermometers
A necessary requirement for every appliance is that it be made of a noncorrosive material. Stainless steel, glass, and certain plastics are the safest materials to put in an aquarium. If an appliance is not available in a safe material, do without it.
Thermometers measure the temperature of the water. Most thermometers for use in the aquarium are filled with mercury, colored alcohol, or colored water. The best is the mercury thermometer. As accuracy is obviously the criterion of a good thermometer, it would be profitable to analyze here what makes a thermometer accurate.
A thermometer works on the principle of an expanding liquid. A calibrated glass tube is used to measure this expansion. Mercury is the most accurate liquid for this purpose, as it expands the most evenly with every rise in temperature. It is obvious that the longer the thermometer, the more accurately it can be read.
Aquarium thermometers are sold in different models. Some are filled with air and float. Other are weighted with lead shot and stand on the bottom of the tank. Still another model is fastened to the side of the aquarium with a suction cup. The easiest to read without removal from the water is the one fastened to the side of the tank, though the standing type can also be set to allow for easy reading.
Since the temperature of a large tank of water is not uniform throughout—it may be 10 degrees warmer at the top of the water than at the bottom—it may be wise to have both a floating thermometer and a standing thermometer. Aeration helps to maintain an even temperature throughout the aquarium.
Do not use boiling water, or even very hot water, to clean the algae off a thermometer, or the thermometer will undoubtedly break. Aquarium thermometers are usually set between 50° and 100° F.; the temperature of boiling water is 212° F. To get the algae off, merely run some steel wool over it a few times and rinse it in some water that has a temperature in the tolerable range of the thermometer.
Most aquarium thermometers are accurate to within about 2 degrees. When comparing the temperature of two or more tanks, use the same thermometer and measure the temperature at the same depth of water.
Heat-sensitive resin strips are usually not very accurate in the long run.
