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Yes, you do! A thermometer is considered an essential piece of equipment in a tropical aquarium. It provides you with an accurate way of measuring the temperature of the water independently of the aquarium heater.
The design of a typical aquarium heater means the heating element is directly underneath the thermostat. This isn’t ideal, as you wouldn’t place the thermostat of a central heating system directly underneath a radiator in a house! This can lead to the heater not reading the true water temperature. Heaters over time can also become uncalibrated from what their temperature is set to and the temperature they heat to. A thermometer, best placed at the opposite end of the tank to the heater, will give you a better reading of the actual temperature.
There are a few different designs of aquarium thermometers:
- Stick on thermometers: placed on the outside of the aquarium, reading the temperature of the water through the glass. Can be affected by outside air temperatures, giving false readings.
- Glass thermometers: Placed inside the aquarium, attached to the glass with a suction cup. More accurate than stick on but can be broken by larger fish. Subject to getting dirty and need cleaning to be able to read.
- Digital thermometers: come in variety of forms, either stuck on the inside or outside, or have a temperature probe on a wire. Give a more accurate reading without needing a scale. Battery operated so need replacing periodically. Be careful with in-tank digital thermometers that the battery cover is on properly to prevent water from damaging the electronics.