The most effective aquarium thermometers on your tank

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Tropical and cold water fish species are both very susceptible to temperature changes in their tank and they will not function well if the water temperature is too cold or too warm. In fact, fish can die from temperature shock. Hence, it is important that you keep your fish comfortable by maintaining the correct water temperature in your aquarium.

A good quality aquarium heater should maintain a constant water temperature. However, the best way to check the temperature is with a reliable aquarium thermometer.

In this guide, we introduce some of the best aquarium thermometers out there, and more!

Best aquarium thermometer reviews

In this part of our guide to the best aquarium thermometers, we've picked six great products for you. Just select your favorite and click to order.

Marina floating thermometer with suction cup

The Marina Floating Thermometer can be attached to the tank wall via the suction cup or just float freely in the water if you prefer.

The thermometer is very easy to read provided you glue it to the front of the tank. The device is pretty accurate and the scale is given in Fahrenheit and Celsius. The temperature sign has a clearly marked safety zone area that is suitable for most species of tropical fish. The thermometer is suitable for both freshwater and saltwater aquariums.

Some users report that their Betta fish flare up on the thermometer and even attack it! Betta owners are therefore best advised to choose a stick-on or digital device rather than a free-floating device.

What we like:

  • To buy cheap
  • Wel-made and durable glass

Room for improvement:

  • The print is small and difficult to read
  • Not exactly

Zacro LCD Digital Aquarium Thermometer


Zacro LCD Digital Aquarium Thermometer Aquarium Water Terrarium Temperature

  • Small volume, big function: the size of the thermometer is 2.17 x 1.46 inches. Our thermometer is suitable for various types of water such as fresh water, tap water, salt water, sea water, etc.
  • Practical: You can choose between Fahrenheit and Celsius, depending on your needs. In addition, each thermometer is equipped with an LR44 battery.
  • Clearly show temperature: You can see the temperature data clearly on the LCD screen. Please note that the thermometer value has a deviation of approx. 1 degree.

The Zacro LCD Digital Aquarium Thermometer provides readings from -58 ° F to 158 ° Fahrenheit via an easy-to-read LCD display. This is a neat, compact unit that we think is very good value for money.

You attach the device to the outside of your tank and place the probe in the water. The thermometer is suitable for use in saltwater, freshwater, and brackish water tanks, and you can expect only a degree of variation in the accuracy of the device. You can set the thermometer to show the temperature in Fahrenheit or Celcius.

What we like:

  • Easy to read
  • Batteries are included
  • Very accurate

Room for improvement:

  • The batteries need to be replaced from time to time

Fluval Wireless 2-in-1 digital thermometer

Fluval Wireless 2in1 Digital Thermometer

  • 2-in-1: Measures water and room temperature exactly within 10 ° C.
  • Wireless technology: no probes or messy cables The large LCD display shows the room temperatures in the aquarium and the surrounding area at the same time
  • Large, easy to read LCD display

Fluval makes very good quality aquarium equipment including pumps, filtration systems, aquariums and thermometers. The Fluval Wireless 2-in-1 Digital Thermometer doesn't disappoint and delivers accurate readings from 68 to 80 degrees Fahrenheit on a large, very clear LCD display that can be easily read from a distance.

A handy feature of the thermometer is that it shows both the room temperature and the tank water. You attach the thermometer to the outside of the aquarium glass and it can be used with both saltwater and freshwater tanks. A product warranty is also included, which is always especially reassuring.

What we like:

  • Easy to read
  • Does not require a probe
  • Easy to use

Room for improvement:

  • The batteries need to be replaced from time to time

Lifegard Aquatics Big Digital temperature alarm


Lifegard Aquatics Digital Temp Alert

  • A digital thermometer with a large display and warning function shows both the water temperature of the aquarium and the room temperature
  • All contain a long-life AAA battery, a plastic probe with a suction cup and cable
  • All models are safe for salt or fresh water

While the Lifegard Aquatics Big Digital Temperature Alert Thermometer isn't the cheapest model you can find, it's extremely accurate. It provides readings from -58 ° to 158 ° Fahrenheit via a very easy-to-read LCD display.

You attach the thermometer to the outside wall of the aquarium and give you the ambient air temperature in your room and the water temperature in your tank in degrees Fahrenheit. The thermometer also has a plastic probe that you can attach to the inside of the aquarium if you want to do so using the plastic suction cups provided. The device is suitable for both freshwater and saltwater fish tanks.

One reason for the comparatively high price of this thermometer is that it offers you four warning functions via flashing LEDs or acoustic warnings that warn you if the water temperature is too low or too high.

What we like:

  • Easy to read
  • Temperature alarm function
  • One year product guarantee

Room for improvement:

  • The batteries need to be replaced from time to time

HDE LCD Digital Aquarium Thermometer

The HDE LCD Digital Aquarium Thermometer has a large LCD display that is easy to read and shows readings from 68o to 80o Fahrenheit.

The thermometer is attached to the outer or inner wall of the tank using suction cups that are supplied with the device. Simply place the probe in the water and get accurate real-time values ​​displayed in both Celsius and Fahrenheit and accurate to 0.1 degrees. The device is powered by LR44 batteries that are included with the device.

What we like:

  • Accurate and reliable
  • Easy to read
  • External probe design

Room for improvement:

  • The batteries need to be replaced from time to time

Cooper Atkins DFP450W Digital Pocket Test Waterproof part

The Cooper Atkins thermometer is not a real aquarium thermometer, but a replacement part for another temperature measuring device. However, this pocket digital thermometer comes in extremely handy when you want to quickly check that your heater's built-in thermometer is working properly or that your permanent thermometer is still accurate.

To test the water temperature, all you have to do is dip the stem of the thermometer into the aquarium and read the water temperature on the LCD display. You can also use the device to check the water temperature when performing weekly partial water changes and adding fresh water to your tank. The device provides readings from -40 ° F to 450 ° Fahrenheit.

What we like:

  • Very accurate
  • Ideal for water changes
  • Handy, portable pocket size

Room for improvement:

  • Cannot be left in the aquarium permanently

What is a temperature shock in aquarium fish?

Why is it so important that the water in your aquarium is at a correct and stable temperature?

Basically, when the temperature drops too low or gets too high, your fish becomes stressed. Stress affects the fish's immune system and makes them vulnerable to attack by bacteria and parasites. A prolonged temperature shock can even kill your fish. It is therefore of the utmost importance to be able to monitor the water temperature in your aquarium.

How to recognize a temperature shock

The symptoms of temperature shock vary depending on whether the condition is caused by water that is too cold or too warm.

Symptoms of cold temperature shock

If the water temperature suddenly falls too low, the fish become very sluggish. This can happen if your heating fails or if an unheated tank is kept in a cool room that suddenly becomes very cold on a winter day, for example.

Fish are ectothermic or cold-blooded. This means that fish cannot generate any body heat for themselves. Instead, the creatures take the warmth they need from their surroundings. If the water is too cold, the fish become immobile and can no longer swim. Sometimes they are completely in a coma on the underground.

You can treat cold water shocks by increasing the temperature in the tank very gradually. Add warm water to the aquarium while checking the temperature. Immediately replace or reset the heater on your tank.

Symptoms of a hot temperature shock

As is to be expected, a hot temperature shock occurs when the water temperature in the aquarium gets too high. This can happen if your heater fails or if your tank is in a position where direct sunlight can shine directly on it.

There are a number of symptoms that can indicate a hot temperature shock:

Difficulty breathing

Fish hang on the surface of the water and breathe very quickly. Warm water does not store oxygen, neither does cooler water. If the water is too warm, the fish cannot breathe and suffocate.

Directly under the water surface there is a small pocket with very good oxygenated water. Therefore, the fish try to stay on the surface where they can breathe more easily.

Irregular swimming

Some species of fish swim faster or more irregularly than normal. These excess energy levels can cause the fish to become stressed, weaken their immune systems and potentially cause health problems.

How to fix the problem

Simply add cooler water to the aquarium and monitor the temperature until the correct level is reached. Check your heater by placing it in a bucket of water and letting the device heat the water. Make sure that the heater is not damaged or defective and replace the device if necessary.

What temperature should my aquarium be?

Aquarium fish are broadly classified as cold or tropical water in terms of water temperature.

Tropical fish generally live in waters where the temperature is consistently above 68o Fahrenheit. Fish classified as cold water species include temperate species that typically require water temperatures between 50 ° and 68 ° Fahrenheit.

In general, aquarium heaters are specially calibrated to a preset temperature range that starts at 68 degrees Fahrenheit and goes up to 86 degrees Fahrenheit. When choosing a thermometer, make sure you choose an adjustable thermometer so that you can set the device to the preferred temperature of your fish.

Different types of aquarium thermometers

There are usually three types of aquarium thermometers to choose from. Each thermometer has its own deviations, advantages and disadvantages, and is suitable for different sizes and styles of aquariums.

Digital thermometers with probes

A digital thermometer has a probe that you place permanently or temporarily in your aquarium. The probe is connected to a digital display device attached to the outside of the tank. You can choose between wireless or wired models as well as mains or battery operated devices.

The digital thermometer is considered to be the most accurate of the models available, but it has some drawbacks:

  • The probe is attached to the display, which doesn't look good.
  • On some models, the sensor and display unit must be placed in the tank. This can be dangerous to your fish if the batteries leak.
  • Some cheaper brands have shorter cables that connect the probe to the display. This can be problematic if you have a large aquarium.

Digital thermometers also have many advantages:

  • Some models have an audible warning feature that warns you if the water temperature falls or rises outside of the range you selected.
  • This type of aquarium thermometer is extremely durable and is not affected by the room temperature.
  • The probe can easily be moved around the tank so that you can check that the water temperature is constant.
  • Digital thermometers are usually much easier to read than other models with old school printed displays.

Submersible aquarium thermometer

Diving aquarium thermometers are designed so that they can be attached to the water with suction cups in the glass, float freely in the water, are weighted so that they sink and rest on the ground, or can be hung on the side of the glass using a clip.

The main disadvantages of submersible aquarium thermometers are:

  • Most are made of glass, so the devices are more prone to damage than other models.
  • The temperature scale is often printed tiny, which makes the device very difficult to read.
  • Unfortunately, dive boats are notoriously inaccurate. So it makes sense to use multiple devices in different areas of the tank so that you get an average temperature reading.

On the positive side:

  • Immersion thermometers have a brightly colored “safe zone” on the scale so that you can see at a glance when the water temperature is outside the desired range.
  • You can place immersion thermometers anywhere you want and they're easy to move too.

Thermometer sticker strips

The starter kits for aquariums often contain adhesive thermometer strips. These devices are extremely popular mainly because they are easy to use and very cheap to buy. The water temperature is displayed digitally via, so that the thermometer is easy to read.

Stick-on thermometers are definitely the cheapest option and generally come with both Fahrenheit and Celcius scales and a fairly wide temperature range. These thermometers stick to the outside of the tank glass.

The main problem with stick-on thermometers is that they are not particularly accurate. The ambient air temperature in the room can often influence the measured value. The aquarium material, the proximity of the thermometer to heat or cooling sources and the position at which you stick the device on the tank also influence the measured value.

Space for an aquarium thermometer

It is very important that the temperature in your aquarium is uniform throughout the environment. Hot and cold spots can affect plant growth and stress your fish. By placing your heater next to the filtration unit or the pump outlet, you can ensure that warm water is pushed right around the entire tank.

To monitor the temperature in a small to medium-sized tank, place a thermometer on the farthest end of the aquarium from the heater. This shows you that the water temperature at the far ends of the tank is correct.

If you have a very large tank, we recommend using multiple thermometers positioned in different places in the aquarium. Alternatively, you can use a probe thermometer and periodically reposition the probe.

You need to be able to read the thermometer easily, so it makes sense to place it on the front of the tank or on an accessible side wall.

Final thoughts

Aquarium fish can suffer from temperature shock if the water temperature suddenly changes. This applies to both cold water and tropical species. To ensure that the temperature in your tank remains constant throughout the environment, you should use a reliable, easy-to-read aquarium thermometer.

All of the aquarium thermometers tested here do the job for you, making sure your fish are comfortable and thriving.

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