Aquarium equipment

The Best Aquarium Thermometers For Your Tank

Last Updated November 17, 2020
Best Aquarium Thermometer

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Tropical and coldwater fish species are both highly susceptible to changes in temperature in their tank, and they won’t do well if the water temperature is too cool or too warm. In fact, fish can die from temperature shock. So, it’s essential 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, but the best way to check the temperature is by using a reliable aquarium thermometer.

In this guide, we review some of the best aquarium thermometers on the market, and much more too!

Best aquarium thermometer reviews

In this part of our guide to the best aquarium thermometers, we’ve picked out six excellent products for you. Simply pick out your favorite and click to order.

Marina Floating Thermometer With Suction Cup

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Marina Floating Thermometer for Betta Fish Tank with Suction Cup, Aquarium Thermometer, 11201A1
  • Easy to read floating aquarium thermometer with suction cups
  • Includes a safety zone indicator appropriate for most tropical fish
  • Equipped with suction cups to attach to the side of your fish tank

The Marina Floating thermometer can be fixed to the tank wall via the suction cup or simply allowed to float freely in the water if you prefer.

The thermometer is very easy to read, provided that you stick it to the front of the tank. The device is pretty accurate, and the scale is provided in Fahrenheit and Centigrade. The temperature reading plate has a clearly marked safety zone range that’s suitable for most species of tropical fish. The thermometer is suitable for use in both freshwater and saltwater aquariums.

Some users report that their betta fish flare at the thermometer and even attack it! So, betta owners may be best advised to choose a stick-on or digital style device instead of a free-floating one.

What we like:

  • Cheap to buy
  • Wel-made and durable glass

Room for improvement:

  • The print is small and tricky to read
  • Not totally accurate

Zacro LCD Digital Aquarium Thermometer

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Zacro LCD Digital Aquarium Thermometer Fish Tank Water Terrarium Temperature
  • Small volume, large function: The size of thermometer is 2.17 x 1.46 in. Our thermometer is suitable for different water types such as fresh water, tap water, salty water, marine water and etc.
  • Convenient: You can choose seither Fahrenheit or Celsius according to your need. What's more, each thermometer is equipped with a LR44 battery.
  • Show clearly temperature: You can read the temperature data clearly in the LCD screen. Please note that the thermometer reading has about 1 degree deviation.

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 reckon is very good value for money.

You fix the unit to the outside of your tank and put the probe into the water. The thermometer is suitable for use in saltwater, freshwater, and brackish tanks, and you can expect just one degree of variance in the unit’s accuracy. You can choose to 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:

  • Batteries must be replaced from time to time

Fluval Wireless 2-in-1 Digital Thermometer

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Fluval Wireless 2in1 Digital Thermometer
  • 2-in-1: Measures water & room temperature accurately within 10C/20 F
  • Wireless technology: no probes or messy wires Large LCD display simultaneously shows aquarium and ambient room temperatures
  • Large, easy-to-read LCD Display

Fluval makes very good quality aquarium equipment, including pumps, filtration systems, fish tanks, and thermometers. The Fluval Wireless 2-in-1 Digital Thermometer doesn’t disappoint, providing accurate readings from 68o to 80o Fahrenheit via a large, very clear LCD display that can be read easily even from a distance.

A handy feature of the thermometer is that it provides readings of both the ambient room temperature and the tank water. You fix the thermometer to the outside of the fish tank glass, and it can be used with both saltwater and freshwater tanks. A product warranty is also included, which is always reassuring extra.

What we like:

  • Easy to read
  • Doesn’t need a probe
  • Simple to use

Room for improvement:

  • Batteries must be replaced from time to time

Lifegard Aquatics Big Digital Temperature Alert

Lifegard Aquatics Digital Temp Alert
  • A large display digital thermometer with Alert feature Displays both aquarium water temperature and room temperature
  • All include a long-life AAA battery, plastic probe with suction cup and cord
  • All models are safe for salt or fresh water use

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

You fix the thermometer to the aquarium’s external wall, and it provides you with the ambient air temperature in your room and the water temperature in your tank, too, in degrees Fahrenheit. The thermometer also has a plastic probe that you can fix to the inside of the fish tank if you want to via the plastic suction cups that are included. The device is suitable for use in both freshwater and saltwater fish tanks.

One reason for t thermometer’this thermometer’ss comparativly high price is tprovidesat it provides you with four alert features via flashing LEDs or sound alerts that warn you when the water temperature is too low or too high.

What we like:

  • Easy to read
  • Temperature alert feature
  • One-year product warranty

Room for improvement:

  • Batteries must be replaced from time to time

HDE LCD Digital Aquarium Thermometer

HDE 2 Pack LCD Digital Fish Tank Aquarium Thermometer Terrarium Marine Temperature (Black)
  • Large easy to read display with easy to apply suction cup for secure convenient placement
  • Submerge probe in to water to measure the aquariums temperature (Do not submerge the display)
  • Accurate temperature readings to within 0.1 degree | Temperature range -50°c~ + 70°c. Operating temperature -10°c~ +50°c

The HDE LCD Digital Aquarium Thermometer has a large LCD display that’s simple to read and gives readings from 68o to 80o Fahrenheit.

The thermometer is fixed to the outside or interior wall of the tank via suction cups that are included with the device. Simply place the probe into the water and receive accurate, real-time readings that are displayed in both Celsius and Fahrenheit and are accurate to 0.1 degrees. The device runs on LR44 batteries that are included with the unit.

What we like:

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

Room for improvement:

  • Batteries must be replaced from time to time

Cooper Atkins DFP450W Digital Pocket Test Waterproof Part

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Cooper Atkins DFP450W Digital Pocket Test Waterproof Part
  • Genuine OEM replacement part
  • Cooper Atkins has built a solid reputation as a leading manufacturer and provider of quality time, temperature, and humidity instruments
  • Uses OEM parts for safety, reliability, and performance

The Cooper Atkins thermometer isn’t a true aquarium thermometer, and it’s actually a replacement part for another piece of temperature measuring equipment. However, this digital pocket thermometer is extremely handy if you want to quickly check that your heater’s heater’s integral thermometer is working correctly or that your permanent thermometer is still accurate.

To test the water temperature, all you need to do is dip the stem of the thermometer in the fish tank and read the water temperature on the LCD display. You can also use the unit to check the water temperature when you’re carrying out weekly partial water changes and adding fresh water to your tank. The unit provides you with readings from -40°F to 450° Fahrenheit.

What we like:

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

Room for improvement:

  • Cannot be left permanently in the aquarium

What is temperature shock in aquarium fish?

So, why is it so important that the water remains at a correct and stable temperature in your fish tank?

Well, basically, if the temperature falls too low or rises too high, your fish will become stressed. Stress compromises the fishes’ immune system, leaving them vulnerable to attack by bacteria and parasites. Prolonged temperature shock can even kill your fish, so being able to monitor the water temperature in your fish tank is of paramount importance.

How to recognize temperature shock

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

Symptoms of cold temperature shock

When the water temperature suddenly falls too low, the fish become very lethargic. That can happen if your heater fails or if an unheated tank is kept in a cool room that suddenly gets very cold, for example, on a winter day.

Fish are ectothermic or cold-blooded. That means that fish can’t generate body heat for themselves. Instead, the creatures take the warmth that they need from their environment. If the water is too cold, the fish become immobile and unable to swim, sometimes laying completely comatose on the substrate.

You can treat cold water shock by very gradually raising the temperature in the tank. Add warm water to the aquarium, checking the temperature as you do so. Replace or reset your tank’s heater immediately.

Symptoms of hot temperature shock

As you would expect, hot temperature shock occurs when the water temperature in the fish tank gets too high. That can happen if your heater develops a fault or if your tank is in a position where direct sunlight can shine directly onto it.

There is a range of symptoms that can indicate hot temperature shock:

Breathing problems

Fish hang at the surface of the water, breathing very rapidly. Warm water doesn’t retain oxygen, as well as cooler water, does, so if the water is too warm, the fish won’t be able to breathe and start to suffocate.

Right under the water surface is a small pocket of very well-oxygenated water. That’s why the fish will attempt to remain at the surface, where they can breathe more easily.

Erratic swimming

Some fish species swim more quickly or erratically than they would normally do. Those excesses of energy can cause the fish to become stressed, weakening their immune system, and potentially causing health issues.

How to fix the problem

Simply add cooler water to the aquarium, monitoring the temperature until it returns to the correct level. Check your heater by placing it in a bucket of water and allowing the unit to heat the water. Make sure that the heater is not damaged or faulty and replace the device if necessary.

What Temperature Should My Fish Tank Be?

Aquarium fish are broadly classified as coldwater or tropical when it comes to water temperature.

Tropical fish generally live in waters where the temperature is constantly above 68o Fahrenheit. Fish that are classed as coldwater species iincludetemperate species that usually need water temperatures tetween 50o to 68o Fahrenheit.

Generally, aquarium heaters are specifically calibrated to a preset temperature range that starts at 68o Fahrenheit and offers a range of up to 86o Fahrenheit. When choosing a thermometer, make sure that you choose an adjustable one so that you can set the device to your fishes’ preferred temperature.

Different types of aquarium thermometers

There are typically three styles of aquarium thermometers that you can choose from. Each thermometer has its own variances, pros, and cons and is suited to different sizes and styles of aquariums.

Digital thermometers with probes

A digital thermometer has a probe that you place inside your aquarium permanently or temporarily. The probe is connected to a digital display device that fixes to the outside of the tank. You can choose from wireless or corded models and from units that are mains or battery powered.

Digital thermometer is considered to be the most accurate of the available styles, but they do have a few disadvantages:

  • The probe attaches to the display, which doesn’t look good.
  • Some models require the sensor and the display unit to be placed inside the tank, which could be dangerous to your fish if the batteries leak.
  • Some cheaper makes have shorter cords connecting the probe to the display, and that could be problematic if you have a large aquarium.

Digital thermometers do have a lot of advantages too:

  • Some models have an audible alert feature that warns you when the water temperature drops or rises out of the range you have selected.
  • This style of aquarium thermometer is extremely hardwearing and isn’t affected by the ambient room temperature.
  • The probe can easily be relocated around the tank so that you can check the water temperature is consistent throughout.
  • Digital thermometers are usually much easier to read than other styles that have old-school printed displays.

Submersible aquarium thermometers

Submersible aquarium thermometers are designed to be placed inside the setup fixed to the glass with suction cups, free-floating in the water, weighted so that they sink and rest on the substrate, or hung on the side of the glass via a clip.

The main disadvantages of submersible aquarium thermometers are:

  • Most are made from glass, so the units are more liable to damage than other styles.
  • The temperature scale is often in tiny print, making the device very difficult to read.
  • Unfortunately, submersibles are notoriously inaccurate, so it’s sensible to use multiple devices set in different areas of the tank so that you get an average temperature reading.

On the plus side:

  • Submersible thermometers do have a brightly colored, “safe zone” marked on the scale so that you can see at a glance when the water temperature is outside the desired range.
  • You can put submersible thermometers wherever you want to, and they are easy to move around, too.

Thermometer sticker strips

You often find stick-on thermometer strips included with aquarium starter packs. These devices are extremely popular, largely because they’re easy to use and very cheap to buy. The water temperature is displayed digitally via, making the thermometer clear to read.

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

The main problem with stick-on thermometers is that they are not terribly accurate. Often, the ambient air temperature in the room can affect the reading. Also, the aquarium material, the proximity of the thermometer to sources of heat or cooling, and where you stick the unit on the tank will also influence the reading you get.

Where to place an aquarium thermometer

It’s very important that the temperature in your fish tank is even throughout the environment. Hot and cold spots can compromise plant growth and stress your fish. So, by placing your heater next to the filtration unit or pump outlet you can ensure that warmed water is pushed right around the whole tank.

small home aquarium with thermometer and fish

To monitor the temperature in a small to medium-sized tank, place one thermometer at the farthest end of the aquarium from the heater. That will show you that the water temperature is correct at the very extremes of the tank.

If you have a very large tank, we recommend that you use several thermometers positioned at different locations around the aquarium. Alternatively, you could use a probe thermometer and reposition the probe regularly.

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

Final thoughts

Aquarium fish can suffer from temperature shock if the water temperature changes suddenly. That applies to both coldwater and tropical species. To make sure that the temperature in your tank is kept even throughout the environment, you should fit a reliable, easy to read, aquarium thermometer.

All of the aquarium thermometers we’ve reviewed here will do the job for you, ensuring that your fish are comfortable and thrive.

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