5 Best Aquarium Thermometers Unboxed, Tested For Accuracy & Compared (2021 Review)

Maintaining the correct water temperature in your aquarium can be the difference between success and failure.

That’s why it’s SO important to be able measure its temperature accurately. And while heaters are great for regulating your tank’s temperature, their readouts aren’t always 100% accurate.

To bring you the best information, I bought 5 different types of aquarium thermometers:

  • JW Pet Company Fusion Smarttemp Thermometer
  • AQUANEAT Aquarium Thermometer
  • Capetsma Aquarium Thermometer with Digital Touch Screen
  • VIVOSUN LCD Digital Aquarium Thermometer
  • Marina Floating Thermometer with Suction Cup

I tested each of them for accuracy, installation, and easy of use (how easy it is to read), to find out which is the best aquarium thermometer.

TL;DR: Our Top Picks For Best Thermometer

After buying and testing 5 thermometers for accuracy and how easy it is read and use, my pick for the overall best aquarium thermometer is the JW Pet Company Fusion Smarttemp Thermometer.

It’s super easy to install and use and it turned out to be the most accurate. When I got done with the experiment I took the other thermometers out of the tank and left the Fusion.

If you’re looking for a digital thermometer, I also highly recommend the Aquaneat as the best digital aquarium thermometer. The LCD is easy to see and this model was proven to be very accurate and consistent.

JW Pet Company Smarttemp Thermometer Aquarium Accessory
JW Pet Company Smarttemp Thermometer Aquarium Accessory
    AQUANEAT 3 Pack Aquarium Thermometer, Reptile Thermometer, Fish Tank Thermometer, Digital Thermometer, Terrarium Water Temperature Test, with Large LCD Display
    AQUANEAT 3 Pack Aquarium Thermometer, Reptile Thermometer, Fish Tank Thermometer, Digital Thermometer, Terrarium Water Temperature Test, with Large LCD Display

      Last update on 2021-10-06 / Commissions Earned / Images from Amazon Product Advertising API

      5 Best Aquarium Thermometers Compared & Reviewed

      Below, you’ll find my reviews and comparisons for different aquarium thermometers I purchased and tested.

      Here are the results:

      1. JW Pet Company Fusion Smarttemp Thermometer (Best Pick)

      1. JW Pet Company Fusion Smarttemp Thermometer

      I have to hand it to JW Pet Company, they make an awesome thermometer. I’ve used this brand for several years now and have always found them handy.

      I knew I already liked this thermometer, but I wanted to be fair and test it out, just like the rest. All three of the Smarttemps I tested showed exactly 32°F (0°C) on the ice bath test.

      For this set of reviews, I tested a brand new one along with two that were already in my tanks. I tested each one twice with the ice bath, so that’s six tests total.

      To be fair, this is an alcohol thermometer and not a digital one, so you don’t get an absolute number readout. But, if you’re just eyeballing it, they look like they’re pretty much dead on. The number scale on the face of the thermometer goes all the way down to 30°F, but the liquid never went below 32°F.

      Installation is super, super simple. You just take the magnet off the front of the thermometer, put the main part of the thermometer in the tank, up against the glass and put the magnet on the outside of the glass, near the top of the thermometer. 

      I’ve never had a problem with this thermometer coming loose or getting moved around the aquarium, even in the tank with my biggest cichlids. 

      As far as reading this thermometer, you do have to bend down and look at the line of red liquid, you can’t just walk by and read it like you can a digital thermometer. But, the numbers and lines are all well defined, making it really easy to read the temp.

      Also, if you need to move the thermometer later on, you just grab the main part from the inside of the tank and the outside magnet and move it to another spot in the tank, easy peasy.

      But, I have one little gripe: if you accidentally pull the magnet off the glass, the main part of the thermometer sinks to the bottom of the tank. I would prefer if it floated, but honestly, it’s only a tiny flaw in an otherwise awesome device.

      Pros: 

      • Very accurate
      • Easy to install
      • Stays in place
      • Easy to move

      Cons: 

      • Thermometer sinks if front magnet is removed
      JW Pet Company Smarttemp Thermometer Aquarium Accessory
      JW Pet Company Smarttemp Thermometer Aquarium Accessory

        Last update on 2021-10-06 / Commissions Earned / Images from Amazon Product Advertising API

        2. AQUANEAT Aquarium Thermometer (Best Digital Aquarium Thermometer)

        2. AQUANEAT Aquarium Thermometer

        Of the three digital thermometers that I tested, the Aquaneat was the most accurate. 

        You install this thermometer by hooking a suction cup on a slot on the back of the temperature module and then running a wired probe into the tank itself, which is secured with another suction cup.

        The temperature module has a nice, easy to read LCD readout. It’s easy to see from multiple angles. You can even read the temp from several feet away.

        I liked this since all I had to do was walk by the tank and I could quickly and accurately figure out the temperature.

        Also, all three Aquaneat thermometers I tested gave consistent temperature readings, all within a tenth of a degree of each other.

        The only little downside to this thermometer is that you do have to stick a good part of your arm into the water to suction cup the temperature probe to the inside glass of the aquarium.

        But, really, it’s not hard to do at all and the suction cups (both in and out of the tank) stayed in place with no problems, even in my crazy busy house on one side of the glass and big active fish on the other side.

        All in all, very impressed with these and I highly recommend them.

        Pros: 

        • Very accurate
        • Suction cups stay in place
        • Easy to read display

        Cons: 

        • Installation requires reaching into the tank
        AQUANEAT 3 Pack Aquarium Thermometer, Reptile Thermometer, Fish Tank Thermometer, Digital Thermometer, Terrarium Water Temperature Test, with Large LCD Display
        AQUANEAT 3 Pack Aquarium Thermometer, Reptile Thermometer, Fish Tank Thermometer, Digital Thermometer, Terrarium Water Temperature Test, with Large LCD Display

          Last update on 2021-10-06 / Commissions Earned / Images from Amazon Product Advertising API

          3. Capetsma Aquarium Thermometer with Digital Touch Screen

          Capetsma Aquarium Thermometer with Digital Touch Screen

          This was the only thermometer I tested that measures the water temperature from the outside of the tank only; there are no probes or other parts of the thermometer that actually make contact with the water itself, just the outside glass.

          Of the five thermometers I tested, this one was the easiest as far as set up. There’s a sticky pad on the back of the thermometer, you just peel off the backing and stick the thermometer to the side of the tank.

          Yep, it’s just that easy.

          But, the one catch is that this thermometer is not as accurate as the other ones I tested. I couldn’t submerge this one in the ice bath since it is not waterproof.

          I did place it up against a glass filled with chilled water and ice, but the lowest it ever showed was 46°F (8°C). I also tried putting a piece of ice directly on the sensor on the back of the unit, which read as 34.7 degrees.

          When I applied the thermometer to my actual tank, it reads about 1.5°F higher than all the other thermometers placed in the same area of the tank.

          So, if you’re looking for scientific accuracy, this is not the thermometer for you. But, it does a good job of giving you a ballpark for your tank temperature. 

          The front of the thermometer has little touch screen controls that let you switch between celsius and fahrenheit. You can also set a high and low temperature range, and if your tank temp goes outside that range, the temp display on the front of the thermometer will flash to alert you.

          I thought this was a super cool feature that could help alert you that something is wrong in the tank.

          But, the biggest downside of this thermometer is that, once it’s been applied to the glass, you can’t reposition it.

          However, I do really like how large the temp display is, although you sometimes have to move side to side a little so you can see the LCD properly.

          Pros: 

          • Easy installation
          • Display flashes if tank is too hot/cold
          • Large temp display
          • Touch screen controls

          Cons: 

          • Can’t move after installation
          • Not as accurate as other thermometers
          capetsma Fish Tank Thermometer, Touch Screen Digital Aquarium Thermometer with LCD Display, Stick-on Temperature Sensor ensures Optimum Temperature in Terrarium, for Your pet Amphibians and Reptiles…
          capetsma Fish Tank Thermometer, Touch Screen Digital Aquarium Thermometer with LCD Display, Stick-on Temperature Sensor ensures Optimum Temperature in Terrarium, for Your pet Amphibians and Reptiles…

            Last update on 2021-10-06 / Commissions Earned / Images from Amazon Product Advertising API

            4. VIVOSUN LCD Digital Aquarium Thermometer

            VIVOSUN LCD Digital Aquarium Thermometer

            This is another digital thermometer with an LCD display that I tested out. The design is very similar to the Aquaneat. But, the Vivosun has a much longer probe wire than the Aquaneat. 

            This could be particularly useful if you have a deep tank or need to place the display module far away from the probe.

            I was again impressed with the strength of the suction cups. I had no problem with having to reapply the suction cups or anything like that. So, once I had it installed, it stayed put.

            My biggest gripe is that these were not as accurate or consistent as the Aquaneat thermometers. The Vivosun came as a 4-pack. I made sure to put all of the temperature probes very close together, but I still had a difference of up to 4°F between the highest and lowest temps. 

            That’s a pretty big margin of error. If you think the tank is at 82°F (28°C), but it’s really at 86°F (30°C), your fish could die.

            Like the Aquaneat, these thermometers have large, easy to read LCD screens. But, if it’s not giving you an accurate temp, who cares how easy it is to see? 

            So, this model looks close to the Aquaneat, but it doesn’t match up.

            Pros: 

            • Strong suction cups
            • Easy to read digital LCD display
            • Long probe wire

            Cons: 

            • Not as accurate/consistent as Aquaneat
            VIVOSUN 4-Pack LCD Digital Aquarium Thermometer Fish Tank Water Terrarium Temperature with Suction Cup for Turtle
            VIVOSUN 4-Pack LCD Digital Aquarium Thermometer Fish Tank Water Terrarium Temperature with Suction Cup for Turtle

              Last update on 2021-10-06 / Commissions Earned / Images from Amazon Product Advertising API

              5. Marina Floating Thermometer with Suction Cup

              Marina Floating Thermometer with Suction Cup

              I remember, what seems like eons ago, when this was the only style of thermometer that you could find in live fish stores.

              So, I was shocked when my analysis made these out to be the worst of the bunch. I guess I thought that the old technology would be more accurate and reliable.

              But, it turned out, I was dead wrong.

              These were the least accurate or consistent of the whole group! 

              I bought a 3-pack of these so I could look for differences. I don’t think they were calibrated properly at the factory because there was a difference of 5°F between the highest and lowest temps!

              Installation is really easy. You just stick the suction cup to the glass just inside the tank. It’s also really easy to move these any time you want. 

              The suction cups did a great job of staying in place. And if the thermometer comes off the glass, it will float, so you can easily retrieve it.

              But, these are also the hardest to read. You have to turn the thermometer just right to see the red line and the numbers are very small. My 43 year old eyes were not thrilled about this.

              So, these are better than nothing, but not by much.

              Pros: 

              • Easy to install
              • Good suction cups
              • Floats if it’s knocked loose

              Cons: 

              • Least accurate/consistent
              • Hard to read
              Marina Floating Thermometer for Betta Fish Tank with Suction Cup, Aquarium Thermometer, 11201A1
              Marina Floating Thermometer for Betta Fish Tank with Suction Cup, Aquarium Thermometer, 11201A1

                Last update on 2021-10-06 / Commissions Earned / Images from Amazon Product Advertising API

                Which Aquarium Thermometer Is Best?

                So, I would wholeheartedly say the JW Pet Company Fusion Smarttemp Thermometer was hands down the best one.

                It’s super easy to install and use and it turned out to be the most accurate. When I got done with the experiment I took the other thermometers out of the tank and left the Fusion! 

                I love that this thermometer is so easy to install and my eyes love that it’s easy to read.

                The magnet does a great job of keeping the thermometer in place, even with a giant Texas cichlid bolting around in there.

                Definitely, if you’re wanting to pick up a new thermometer, I would go with this one.

                If you’re looking for a digital thermometer, I also highly recommend the Aquaneat. The LCD is easy to see and this model was proven to be very accurate and consistent.

                So far, the boisterous fish and the crazy cats and dogs haven’t managed to knock the suction cups off the glass at all. Believe me, that’s an accomplishment all on its own.

                I had a lot of fun doing this experiment!

                I hope you find this information helpful.

                I wish you and your fish the very best!

                JW Pet Company Smarttemp Thermometer Aquarium Accessory
                JW Pet Company Smarttemp Thermometer Aquarium Accessory
                  AQUANEAT 3 Pack Aquarium Thermometer, Reptile Thermometer, Fish Tank Thermometer, Digital Thermometer, Terrarium Water Temperature Test, with Large LCD Display
                  AQUANEAT 3 Pack Aquarium Thermometer, Reptile Thermometer, Fish Tank Thermometer, Digital Thermometer, Terrarium Water Temperature Test, with Large LCD Display

                    Last update on 2021-10-06 / Commissions Earned / Images from Amazon Product Advertising API

                    Ice Bath Test: How We Measured Thermometer Accuracy

                    thermometer ice bucket test

                    The ice bath method is the safest and most reliable method for testing the accuracy of a thermometer.

                    An accurate thermometer will read 32°F (0°C) in an ice bath at any elevation. Water boils at different temperatures depending on elevation, so the ice bath is a better test.

                    The nice part is that it’s actually pretty easy to test thermometers this way and the equipment needed is just everyday household items.

                    Equipment:

                    • 20 oz open topped plastic container 
                    • Chilled water from the refrigerator
                    • Ice cubes
                    • Metal spoon

                    Steps:

                    1. Add ice cubes to the top of the container.
                    2. Fill the container with water chilled in the refrigerator for several hours.
                    3. Stir the ice water in the container for at least 15 seconds.
                    4. Insert the thermometer into the ice bath. Keep the thermometer moving so that it is not just resting against the ice or the side or bottom of the thermometer.
                    5. Check the temperature reading. An accurate thermometer should read 32°F (0°C). If not, take note of how many degrees off the temperature reading is.

                    Just to be fair, we tested each thermometer twice. We also tested multiple thermometers of each kind to make sure they showed consistent results.

                    We DID NOT Use Boiling Water

                    There are several reasons we didn’t use the boiling water method to test the thermometers.

                    • Aquarium thermometers aren’t meant to handle boiling water and could melt
                    • The boiling point of water varies depending on the altitude and atmospheric pressure
                    • Boiling water can cause severe burns and I’m really clumsy

                    Given all these factors, attempting to test using boiling water was just too risky. And we really don’t recommend ever using an aquarium thermometer with boiling water.

                    How We Ranked Our Choices

                    I went with three different criteria to determine my rankings and top choice:

                    • Accuracy – how did the thermometer perform in the ice bath test?
                    • Installation – was it easy to install the thermometer?
                    • Ease of Use – does the thermometer stay in place once you’ve installed it? How easy is it to read the display?

                    I ranked each category on a scale of 1-5, with 1 being worst and 5 being best.

                    What to Look for When Choosing a Thermometer for Your Aquarium

                    aquarium thermometers

                    There’s more to picking a thermometer than just aesthetics. Here are some factors to consider.

                    How Easy is it to Use and Install?

                    Most thermometers are fairly easy to install, but some require you to get wetter than others.

                    Some you can just stick on the outside glass while others require you to stick your whole arm in the tank or maybe even partially drain the tank so that you can reach the right spot.

                    None of the thermometers I tested are terribly difficult to install, but I did want to consider  installation as part of the rankings.

                    Accuracy

                    This is probably the most important aspect of a thermometer. I mean, who cares if it’s easy to install and read if it’s giving you the wrong temp?

                    And since a 3°F difference can have huge impacts on your tank, you want the most precise measurement you can get.

                    Durability

                    Even though thermometers tend to be inexpensive, you still want something that’s going to last and stay accurate.  Look for long-lasting durable materials and a good battery life.

                    And if you buy a classic mercury thermometer, you’ll want one that’s not likely to crack or break and is fully submergible.

                    Leaking mercury into you tank will have devastating effects. Digital aquarium thermometers should come with a probe attached to an LCD display. And it’s always a bonus if it includes extra batteries.

                    Temperature Display Readability

                    Some thermometers are super easy to read while others require me to get a flashlight and a magnifying glass so that I can see the numbers clearly. (give me a break, my eyes ain’t what they used to be)

                    Since I have so many tanks to check on during the day, I don’t want it to be a huge pain to read the darn things.

                    So I definitely want a thermometer that’s going to be quick and easy to read day in and day out.

                    One Last Thing… It’s Kind of Important

                    If, for any reason, your aquarium temperature strays far outside the recommended range for your fish.

                    DO NOT try and adjust it quickly.  Sudden changes in temperature can be harmful to your fish and can sometimes lead to death. You should gradually add warm or cold water (depending on the change) to your tank so your fish can acclimatize.

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                    Katherine Morgan
                    Hey, there! I'm Katherine from Northwest Florida. A nunchuck specialist, I've kept aquariums for over two decades, enjoy experimenting with low-tech planted setups and an avid South American cichlid enthusiast. If You'd like to see more of my tanks, check out my Instagram