Aquarium Thermometer Guide


Maintaining proper temperature of your aquarium is very important, especially for tropical tanks. These fish tanks require specific water temperatures, and a good aquarium thermometer will help monitor it.

While an aquarium heater is used to control the water temperature, the aquarium thermometer will help monitor the temperature. It is true that most aquarium heater have a fairly reliable thermostat, which will maintain the water temperature at a certain range. In some cases, the aquarium heater will have a temperature display as well. However, it is not wise to rely on the aquarium heater alone. Since maintaining water temperature is critical to the life inside the aquarium, a thermometer should be used to monitor the water temperature separately.

Types of Aquarium Thermometers

There are many different types of aquarium thermometers. While all aquarium thermometers are used to monitor the water temperature, there are many different types of aquarium thermometers with different features available.

Aquarium Thermometer

Strip Thermometer

Strip thermometers, also known as sticker thermometers, are inexpensive and easy to install. Since the temperature reading is given by the changing color of the liquid crystal ink, it is also referred to as a liquid crystal display or LCD thermometers as well. However, these are not to be confused with digital aquarium thermometers.

Strip thermometers usually do not cost more than a few dollars, and they are often included in fish tank kits. The backside of the strip thermometer comes with an adhesive. This allows you to stick the thermometer anywhere on the external aquarium wall. To install, simply wipe down the aquarium glass. Next, peel the adhesive sticker off the strip thermometer and press it against the glass wall. Most people will stick the thermometer on the edge or side of aquarium so it will not obstruct their view of the fish.

Strip thermometers are popular because they are inexpensive and easy to install. However, they are not the most accurate thermometers. Since they are designed to be installed on the external wall of an aquarium, the outside temperature can affect the temperature display. For example, if direct sunlight is hitting the strip thermometer, it can give inaccurate readings. Strip thermometers placed near AC vents can also give unreliable readings.

Glass Thermometer

Glass thermometers are one of the most common type of aquarium thermometers. They are considered one of the classic styles of aquarium thermometers, but due to their reliability and versatility, they remain relevant to this day.

While glass thermometers are inexpensive, they are fairly accurate. They are usually equally inexpensive or only slightly more expensive than strip thermometers. However, glass thermometers generally provide more accurate readings because they are placed inside the aquarium. The temperature readings are not affected by the outside temperature.

Glass thermometers are very versatile. Based on the different attachments, a glass thermometer can be installed in multiple ways.

Floating Thermometer

If the glass thermometer is attached to a floating device, it can be used as a floating thermometer. This will allow you to install the thermometer near the surface of the water, regardless of the water level.

Keep in mind that most glass thermometers will float on its own, but without a proper attachment, it will not float upright.

There are disadvantages to a floating thermometer as well. As the thermometer floats near the water surface, it can get pushed to the back, and make it difficult to read. In addition, the glass thermometer can be more prone to breaking if it is floating freely. For example, the floating thermometer can get caught in the current of the filter output, and clash against the aquarium wall.

Standing Thermometer

If the glass thermometer is attached to a weighted base, it can be used as a standing thermometer. It can be installed on the bottom of the aquarium, partially buried in the gravel. When the aquarium glass is curved, it can be difficult to install the thermometer on the glass wall. In such cases, a standing thermometer can be useful.

While a standing thermometer is weighted, it can be easily pushed around by a larger fish. Therefore, you may need to fix the position of the thermometer regularly.

Submersible Thermometer

If the glass thermometer is attached to a suction cup, it can be used as a submersible thermometer. This is the most common way to install a glass thermometer. While it can be moved around as needed, it has a fixed position, so it is much easier to read and manage. This is the recommended method of installing a glass thermometer for most aquariums.

Digital Aquarium Thermometers

Digital aquarium thermometers are generally more expensive, but they are the most accurate types of thermometers. They can provide accurate reading to 0.1°F, something that is not possible with an analog thermometer.

There are many different models available, but most take the temperature from a meter that is installed inside the aquarium. Therefore, the temperature reading is not affected by ambient room temperature. In addition, most digital thermometers are manufactured without glass components, making them more durable than many fragile glass thermometers.

Since most digital aquarium thermometers run on batteries, you will be required to change them regularly.

Some digital thermometers have internal displays, while others have external displays. While most digital thermometers are manufactured to good standards, keep in mind that there is a risk of battery leakage. Choose a digital thermometer with an external display if possible.

Alert features are available in some high-end digital thermometers. This can be a useful feature, especially if you have multiple tanks to monitor.

Digital Laser Infrared Thermometer

A digital laser infrared thermometer is a hand-held tool that allows you to point and measure the temperature of the water temperature. It is not installed to an aquarium as a fixed thermometer, but it can be useful as a secondary thermometer.

For example, an infrared digital thermometer can be useful when performing water changes to your aquarium. You can simply point the thermometer to the water in the bucket, and quickly measure the water temperature before adding it to the aquarium. A stick thermometer would be able to perform a similar function, but infrared digital thermometer can measure the temperature without any contact. This will eliminate the risk of contamination between different fish tanks.

Where to Place a Thermometer in a Fish Tank?

An aquarium thermometer must be placed on the opposite end of an aquarium heater. By placing the thermometer away from the aquarium heater, you will be able to get an accurate temperature reading of the entire fish tank. Do not place the aquarium thermometer adjacent to an aquarium heater. The water temperature surrounding the heater may be warm, but there is a possibility that the other side of the fish tank is not the same temperature.

Aquarium thermometers should be placed on the towards the front of the fish tank for easy reading. It can be placed on the side walls as well. Do not place an aquarium thermometer in the center of an aquarium. An aquarium thermometer is important, but you do not want it to be the center focus of your aquarium.

In addition, different types of thermometers will have different placement requirements. Here are some of things to consider when placing a thermometer in a fish tank:

  • For strip thermometers, do not place the thermometer in direct sunlight or AC units. This can affect its reading accuracy.
  • For standing thermometers, keep the thermometer above the gravel line. Only submerge the weighted base component. Submerging the thermometer unit can affect its reading accuracy.
  • For digital thermometers with external components, make sure the wires have a drip loop for safety. The drip loop will prevent any water from reaching the electrical components.

Are aquarium thermometers accurate?

Some aquarium thermometers are not very accurate. They may have been manufactured with a flaw, or it may have started to malfunction over time.

The easiest way to verify the accuracy of your aquarium thermometer is to use a secondary thermometer. If you are measuring the temperature of the same water, you should be get the same temperature readings.

Another way to verify the accuracy of your aquarium thermometer is to place the thermometer in a glass of ice water. Stir the ice water and submerge the thermometer in the water for at least 15 seconds. The thermometer should give the reading of 32 °F.

If the temperature reading is not accurate, you may need to calibrate the thermometer. Some digital thermometers will allow you to reset the thermometer or replace the probe. Unfortunately, glass thermometers with mercury cannot be re-calibrated. These will need to be replaced if the temperature reading is inaccurate.

Fish Laboratory

With decades of collective fishkeeping experience, we are happy to share the knowledge that we've picked up along the way. Our goal at Fish Laboratory Aquatics is to keep publishing accurate content to help fishkeepers keep their fish healthy.

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