Best Aquarium Thermometer in 2021

By Garrison Hickles Updated

Yes, thermometers are required at household for more than just figuring out whether you are suffering from fever or not. If you have an aquarium at your home, then you will need to get yourself an aquarium thermometer because maintaining the right temperature of the tank water can be the difference between the life and death of your aquatic pets and plants.

Choosing the right thermometer requires detailed knowledge of their functionalities and what exactly you want them for. Therefore, we have brought in for you a detailed buying guide of aquarium thermometers wherein we are not only going to list out the best ones available in the market but we also tell you as to why you need them, what are their types and what are the aspects you need to keep in mind before making your purchase.  So, let’s get straight into it starting with the benefits of an aquarium thermometer.

Benefits of an Aquarium Thermometer

First of all, if your aquarium heater comes with a thermometer or temperature reader of its own, then you don’t have to buy an aquarium thermometer separately. However, if it is not the case, you would need to buy one.

You need to understand that different aquatic pets and plants have different needs for the temperature of their tank water since they come from varied habitats. It is important to provide them with the exact temperature so that they can survive. For this, you require a heater. But a heater without a thermometer is as good as a lock without a key. How else are you going to monitor the temperature of the water if you can’t read the temperature?

This is why having an aquarium thermometer is crucial.  It will not only help you keep a close watch on the temperature of the tank water, but you will also be able to know if the heater is working properly or not.

Sometimes, the thermometer that comes with the heater is not of the best quality. So, it may give you a wrong reading of the temperature. So, just to be extra sure, we suggest you buy a thermometer for the safety of your aquatic pets and plants.

Things to Keep in Mind before Buying an Aquarium Thermometer

If you want to have your purchase be worth it, please keep in mind the following things before buying an aquarium thermometer:


Invest in an aquarium thermometer that has a strong built since you would want it to last long. A highly durable thermometer might be a bit expensive but it will be worth the money.

You don’t want your thermometer to crack or break out and leak mercury inside the water (in case of a submersible thermometer) since it will prove fatal to the life of your aquatic pets and plants.


If you can’t read the temperature of your tank water properly on your aquarium thermometer, what good is it? So, make sure to check out that the thermometer that you are buying has a clear temperature readability. We recommend you to go for a thermometer with a probe and LCD temperature display.

That being said, mercury or colour changing crystal thermometers are also great picks. Also, it is better to choose a thermometer that displays temperatures in both Celsius and Fahrenheit since you don’t want to calculate and convert every time you look in your thermometer.

Range and Accuracy

Please note that the chances of finding a thermometer that gives you the exact temperature are highly unlikely. Usually, thermometers often come with a warning in their packaging regarding their accuracy and range. We suggest you opt for thermometers that have an accurate reading within at least +/- 1° C or +/- 2° F.

In addition, the range of temperature is also important. For an aquarium, having a thermometer with the ability to read temperature between 10° C (50° F) to 40° C (104° F) should get the job done.


Maintaining an aquarium is no easy feat and on top of that, you have to take care of multiple apparatus related to it. So, the last thing you want in your aquarium thermometer is a complicated setup. Therefore, buy one that is not only easy to install but is also easy to use.

The best ones are the ones that you can just place in your tank and not worry about anything. However, digital thermometers would require a few additional steps of installation and maintenance (such as battery changes), but still, try and not go for extremely fancy or complicated settings.

Another major aspect that must be noted is the type of thermometer you buy. This is a broader subdivision and requires a section of its own. So, here it is.

Types of Aquarium Thermometers

Take a look at the different types of aquarium thermometers so that you know which one will be best suited for your needs.

Digital Aquarium Thermometers

Digital aquarium thermometers are the most preferred and recommended ones since they are the easiest to read. They come with a probe and a digital display from where you can read the temperature. They are connected to each other through a wire, although some are wireless too. Usually, they are not affected by the ambient room temperature.

Some digital thermometers run through power while others run on batteries. Some expensive ones even come with an alarm that goes off whenever the temperature of the tank drops or rises from the preferred range. They are usually robust and have a strong built.

Stick-on Aquarium Thermometers

Stick-on aquarium thermometers are also known as adhesive strip aquarium thermometers. Evident from their name, they are stuck to the outside body of the tank. As you can understand, this means that they are not the most reliable ones out there for getting an accurate temperature reading.

They usually are thin, flexible strips, although sometimes can feature an LCD. Don’t confuse this with digital aquarium thermometers.  If you are buying a stick-on thermometer, make sure your tank is not near sunlight or heater or any vent that may affect the reading of the temperature.

Standing/Floating Aquarium Thermometers

These are analogue thermometers and reading the temperature from it can sometimes be difficult. However, many manufacturers are providing colour zones on these thermometers. This means that whenever the temperature goes off the preferred range, you can simply tell it by looking at which colour zone the scale is on.

You either have to submerge the thermometer in the tank water or you have let it float on the water surface. Some of them feature a suction cup so that you can keep them in a specified place in your tank. Some are magnetic and you can keep them in a specified space inside your tank by sticking it with a magnet from outside. You can even weigh down the free-floating thermometers if you choose, but be sure to not put too much pressure on them.

The concern with these standing or floating aquarium thermometers is that they are mostly made of glass, which makes them fragile. So, try and look for those that are made from stainless steel or plastic. You also won’t get a digital reading on them. These are comparatively inexpensive ones.

Okay, with the essentials of aquarium thermometer now known, let us dive into some of the best ones available online.

Best Aquarium Thermometers You Need to Buy

After testing out dozens of aquarium thermometers, we came down with the following ones since they proved highly functional and stood out from the rest. Here are the best aquarium thermometers for you.

KollerCraft TOM Temp Alert Digital Thermometer for Aquariums

The KollerCraft TOM Temp Alert Digital Thermometer for Aquariums is one of the most expensive ones available, but for all the right reasons. Measuring 7.5*5*1.5” and weighing in just 1.6 ounces, these are highly compact and can be used for both saltwater and freshwater tanks.

This digital thermometer not only shows you a clear reading of the current temperature but also warns you whenever the temperature goes beyond the pre-set temperature range of 23-27° C (75-82° F). Yeah, we wish the temperature range was a bit wider, but it is what it is. Anyways, it also gives you an audible warning so that even if you missed looking at the temperature, you still would get warned when the sound goes off.

Attached through a 3-feet cord to a plastic probe, it also comes with a suction cup which you can attach anywhere inside the wall of your fish tank. You can run it with either two LR 44 button cells or two Energizer 357 button cells.


  • Clear display
  • High level of accuracy
  • Audible warning when the temperature of the tank water goes off range
  • Suitable for both saltwater and freshwater tanks
  • Comes with a suction cup
  • Features a long 3-feet cord


  • The pre-set temperature range is not wide enough

LCR Hallcrest A-1005 Liquid Crystal Aquarium

If you are looking for a simple stick-in aquarium thermometer, then you should definitely opt for LCR Hallcrest A-1005 Liquid Crystal Aquarium. Extremely easy to read due to its colour-changing liquid crystals, this thermometer gives you a pretty accurate temperature read.

It uses the peel-and-stick design and you can mount it anywhere outside the tank wall as long as it is below the waterline.  Another great feature about this aquarium is the fact that you can remove and reposition it anytime you want. It is best suited for small aquariums.


  • Colour-changing liquid crystals enable easy reading of the temperature
  • Durable
  • Easy to install
  • Removable and repositionable


  • Doesn’t function well in large tanks

American Thermal Aquarium Thermometer

Next up on our list of the best aquarium thermometers is the American Thermal Aquarium Thermometer that features highly sensitive colour-changing liquid crystals.

Similar to the previous one we mentioned on this list, this thermometer also uses a peel-and-stick design which is extremely easy to install. All you need to do is release the paper and mount the thermometer outside the tank wall below the waterline. This allows you to remove and reposition it anywhere outside the tank, and you don’t have to worry about it losing its stickiness.

It has a strong-built and is non-corrosive by nature meaning it will last very long. It is also non-toxic. However, it only features the temperature reading in Fahrenheit, which might be inconvenient for some.


  • Unbreakable
  • Non-toxic
  • Easy to install
  • Colour-changing liquid crystals enable easy reading


  • Suited for small tanks only
  • Only provides temperature read in Fahrenheit

Lifegard Aquatics Digital Temp Alert

Measuring 4”*4”, the Lifegard Aquatics Temp Alert is another excellent aquarium thermometer up for grabs. Its huge screen makes it easy for you to read the temperature through its LCD characters.

An absolute delightful fact about this thermometer is that it not only showcases the temperature of the tank water but it also tells you the room temperature.  While the probe measures the temperature of the tank water, the internal thermometer measures the room temperature.

Moreover, it also alerts you whenever the temperature rises or falls from the desired level. It is suited for both freshwater and saltwater tanks. The in-take probe also comes with a suction cup which you can use to attach it to the aquarium wall. It is powered by one AAA battery, which is included in the packaging.


  • Large screen ensures easy readability
  • Alerts you whenever the temperature of the tank water drops or rises from the preferred range
  • Measures both room temperature and tank water temperature
  • Suited for both freshwater and saltwater tanks
  • Suction cup included


  • Expensive

Zacro LCD Digital Aquarium Thermometer

The Zacro LCD Digital Aquarium Thermometer also finds itself in our list of the best aquarium thermometers due to its high effectiveness. It is considered to be one of the best budget digital thermometers out there.  

Featuring an LCD, its accuracy of temperature is within +/- 2° F. It comes with a probe that you can submerge in your fish tank and you can attach it to the outside wall of your tank with the help of the suction cup that it comes with. It measures 2.1*1.4”, making its compact and less space-consuming.  Its temperature range is also extremely wide -50 to 70° C (32 to 158° F).

It runs on a single LR44 battery which is long-lasting as well as very easy to replace. Besides, it is suitable for both saltwater and freshwater tanks.


  • Clear LCD
  • Easy installation
  • Extremely wide temperature range
  • Suitable for both saltwater and freshwater tanks
  • Allows you to choose between Celsius and Fahrenheit setting


  • Suction cup could have been stronger


When you are rearing aquatic pets and plants, it is your responsibility to provide them with the utmost care. It is crucial to replicate as much of their natural habitat as possible. The temperature of the water that they live in the wild is essential for their existence. So be sure to keep an eye on the temperature of your tank water. And to do that, you would need the help of an aquarium thermometer.

It must be noted that if your aquarium is very large, then you might have to use multiple thermometers at multiple places since the temperature of the water may or may not be the same everywhere in the tank.

So, keep in mind our buying guide and our recommendations of the aforementioned aquarium thermometers before making your final choice.

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