Glass Aquarium Thermometer

The Glass Aquarium Thermometer is the classic instrument for aquarium temperature measurement, using a coloured alcohol column inside a sealed glass tube calibrated in Celsius and Fahrenheit. A suction cup mount attaches the thermometer to the inside of the aquarium glass, keeping it submerged and visible for regular reading.

Despite its simplicity, the glass thermometer remains widely trusted for its zero power requirement, instant availability, and absence of electronic failure modes. Accuracy is typically ±1°C, sufficient for routine aquarium monitoring of most species.

The thermometer should be positioned in good water flow away from heater outlets, which create localised hot spots that produce artificially high readings. It is a reliable backup device for any aquarium, regardless of whether digital or electronic temperature monitoring is also used.