What Is The The Most Accurate Fish Tank Thermometer?

Having an accurate, quality aquarium thermometer might be the difference between life and death for your fish.

You always need to know the exact temperature of your fish tank to ensure it’s within the ideal parameters for your fish.

Accuracy and reliability are the main features you need to worry about when buying a new thermometer, so reading the reviews is important.

For example, here are the best sellers on Amazon – these have the most positive reviews over time.

Best Water Thermometer

Small Tank Thermometer

  • Cheap digital thermometer
  • For use in salt or fresh water
  • Set to Fahrenheit or Celsius
View On AmazonView On Chewy

Digital Touch Screen Thermometer

  • Best-seller: accurate and easy to read
  • Sticks to the outside of aquarium
  • Digital LCD display
View On AmazonView On Chewy

Marina Standing Thermometer

  • In tank thermometer - sinks to the bottom
  • Will remain standing - temp in °C or °F
  • Green safe zone shows best temperature range
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It can be a good idea to have a couple of thermometers (especially in a large tank) in order to check them against one another. If one fails you’ll be able to pick it up sooner.

Many years ago, when I was first starting out keeping fish, I didn’t have an accurate aquarium thermometer and I didn’t check the water temp regularly.

I remember walking past my tank and noticing my fish were all swimming so slowly, but I didn’t think much of it at the time and didn’t investigate any further.

It wasn’t until the next day, when one of my favorite fish, ‘Little Moe with the Gimpy Fin’ was floating upside down, that I took a closer look.

I discovered that the small aquarium heater that was heating the tank had come unplugged from the wall socket.

Little Moe, who had a birth deformity leaving him with a crippled tail, and who was a weak, poorly fish, was first to go. He succumbed to the cold.

This could have been prevented if I had an aquarium thermometer in place.

Perhaps when I noticed that my fish were lethargic I would have checked the thermometer and Little Moe would still be with us.

Don’t let what happened to Little Moe happen to your favorite fish – get the best fish tank thermometer for your aquarium today.

Aquarium thermometers are very cheap, usually only costing a few dollars, so it’s not going to break the bank.

From time to time, ensure they are working correctly in your tank. In the case of a digital fish tank thermometer, make sure that the battery has not gone flat.

1. ZACRO Small Aquarium Thermometer

cheap fish tank thermometerVIEW ON AMAZON →

The Zacro Digital Fish Tank Thermometer is the best-selling aquarium thermometer.

It is a very cheap product that has a probe that is submerged in the fish tank so that you have a constant reading. The display and body of the thermometer should not be put in the water.

Features include:

  • Temperature readings in both Fahrenheit and Celsius
  • LCD screen – clearly shows the current temperature
  • Single power button – when turned on it will take immediate readings
  • Suction cup – doesn’t come loose easily
  • Approx. 38-inch long cable – hide the probe down the back and have the display up front
  • Comes with battery for immediate use – recommended to change each year
  • A 24-month warranty – in most cases it will last a lot longer than this

It has sold many thousands of units and been tried and tested in all sorts of tanks.

After all this, it has been reviewed very positively and has a high star rating.


  • Extremely cheap
  • Small and easy to install
  • Easy to read digital display
  • Readings to 0.1 degree accuracy


  • Not the most quality construction
  • Won’t last a lifetime

2. Touch Screen Digital Aquarium Thermometer

no battery aquarium thermometer

The Capetsma Touch Screen Thermometer is another very popular product for getting accurate temperature readings.

It comes with a CR2032 battery already installed, so it’s ready to go right away.

The image above makes this device look flat, and it almost is!

The dimensions are 3-inches by 3-inches and it’s 0.28-inches thick – a very small profile.

Other features include:

  • Touch-screen display
  • Switch between C and F readings
  • Sticks to aquarium glass or acrylic
  • Large temperature display
  • Transparent screen

It’s not hard to see why so many people choose to buy this fish tank thermometer. It does have a lot going for it.

Most of all, I like that it doesn’t have any cords or probes whatsoever. The battery is in the device, it sticks to the aquarium, and that’s all there is to it.


  • Cord-free
  • Transparent digital LCD display
  • Small and thin
  • Very simple operation
  • Can be used on all tank types


  • The extra features and cool design make it a bit more expensive than the alternatives

3. Marina Standing Thermometer

accurate aquarium thermometers


The Marine Standing Thermometer is another great option – and it’s another design.

We’ve had a corded-probe thermometer, a stick-on thermometer, and this is an in-tank, fully submerged, standing thermometer.

Other than that, thermometers are really all the same, aren’t they?

Nonetheless, the features are:

  • Remains standing upright in the tank
  • Accurate and easy to read (though maybe not as easy to read as digital display models)
  • Safety zone indicator for tropical fish
  • Fahrenheit and Celsius readings
  • Good for both salt and freshwater

The potential downsides of this thermometer are that it could break in the tank (unlikely, but possibly), it takes up precious room inside the tank (not much, but still, some), and it needs to be fully submerged.

In saying that, it’s a super popular design and those who have it seem to really love it.


  • Looks cool standing up unaided in the tank
  • Accurate temperature measurements
  • Tends to stay in the same spot


  • Could potentially break
  • Takes up space in the tank
  • Could be harder to read than other thermometers

4. Thermal Aquarium Thermometer

best aquarium thermometer

The American Thermal Liquid Crystal Thermometer is another popular aquarium thermometer.

This one is applied horizontally to the side of your aquarium and takes reading through the glass.

Many tests of this product find that this is not the most accurate temperate gauge, however, it is consistently inaccurate (if you know what I mean?).


  • Color-coded
  • Peel off and re-stick elsewhere on the aquarium
  • Approx. 5 inches by 3/4 inch

Depending on the construction of your tank (glass or acrylic), it can be two or 3 degrees out, but it will always be out this much so you can factor that in when checking your water temperature.


  • Doesn’t take up space in tank
  • Cheapest option (can buy in packs of 3)
  • Can be shifted
  • Can be hidden discretely at the back of the tank
  • Nothing to break
  • Easy to read


  • Not the most accurate
  • Less effective on plastic/acrylic tanks
  • Doesn’t always stick well

5. JW Pet Fish Tank Thermometer

most accurate aquarium thermometer

The final fish tank thermometer we recommend here today is the JW Pet Company in-tank thermometer.

This product is secured to the inside of your tank with a magnet placed on the outside.

Features include:

  • High accuracy of +/- 2 degrees
  • Easy to read temp
  • Fahrenheit & Celsius
  • Made of glass
  • Cheap fish tank thermometer

I like that it has the ‘green zone’ so that you know if your tank is kept within the ideal temperature for most tropical fish.

However, this could be confusing if your tank needs higher or lower parameters. If so, you should avoid this choice.


  • Easily place in tank with magnet
  • Doesn’t require glue or suction
  • Affordable


  • Can be shifted by stronger fish
  • Some units have been found faulty and unreliable

Best Aquarium Thermometer

cheapest fish tank thermometer

What should you be looking for in an aquarium thermometer?


Obviously, it’s most important that it be accurate, otherwise what’s the point!

Most thermometers are not going to have a problem with this.

If you have a digital thermometer you just need to make sure that the battery does not start going flat and giving inaccurate results.

Design and Aesthetic

You want a tank thermometer that looks good or which can be completely hidden away.

This will be easier to do if you have a 55-gallon fish tank for example, but more difficult if you’ve only got a 3-gallon tank.

Safe For Fish

Another obvious feature we want to have in our tank thermometers is that they are safe for fish.

Water thermometers should be non-toxic and non-chemical leaching.

Any glass thermometer should be shatter-proof.

Accurate Aquarium Thermometers

most accurate aquarium thermometer

I hope you’ve been able to find the right thermometer for your setup.

Let us know in the comments below what your favorite thermometer is, and why you like it so much.

Also, if you’ve had any issues with the tank thermometers we’ve listed here today, let us know!

While we’ve been able to test out some of the options, we haven’t tried all of them. Reading the reviews is a great help in making that final decision.

The Zacro Thermometer has been the best option for many. It has a lot of great features and can be trusted over time to provide accurate readings.

The Capetsma thermometer is a good alternative and my personal favorite. I like that there are no cords and the design is cool.

Whichever you decide on, just make sure you get it set up soon.

It may help you to determine whether or not you need a new heater or perhaps, for those in warmer climates, an aquarium cooling device.

Some people even set their tank up with a thermostat that can control multiple different devices depending on water temperature measurements.


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