Which aquarium thermometer is best?

Keeping an aquarium is a rewarding hobby. Tropical fish, with their brilliant colors and curious behavior, provide hours of relaxing entertainment and ambiance.

However, fish are fragile creatures that need to be carefully monitored to keep them in good health. An aquarium thermometer is one of the most critical pieces of equipment for keeping tabs on your fish’s living conditions.

The Aquaneat Digital Aquarium Thermometer Set offers digital accuracy and a large LCD. This pack of three thermometers is great for those with more than one tank.

What to know before you buy an aquarium thermometer

Your fish’s requirements

Most tropical fish need a consistent water temperature between 75 to 80 degrees Fahrenheit to thrive. Needs vary between species, so research your pet to know what range is best for them. If you have multiple fish in the same tank, make sure they have similar temperature requirements.

Aquarium thermometer types

  • Glass thermometers are similar to those you would expect to see hanging outdoors. They contain colored fluid that rises or falls to indicate the temperature of your aquarium. They either float freely or adhere to the interior glass of your tank with a suction cup. 
  • Digital thermometers feature an LCD. Some are completely submersible, but most sit outside your aquarium with only a probe at the end of a long cord under the water. They’re accurate and easy to read but more expensive than other options. They require batteries or a wall outlet for power.
  • Liquid crystal thermometers adhere to the outside glass of your aquarium and display the temperature by changing colors. These thermometers are the least expensive, but they are not recommended. They are inaccurate, can’t be moved once installed and are hard to read.

Thermometer placement

Choose an aquarium thermometer that gets submerged in your fish’s water. Those that stick to the outside of the glass are affected by the temperature of the room your tank is in and are therefore not as accurate. 

Your tank will be warmest near the heater, so install your thermometer on the opposite end of the aquarium to make sure the entire tank is being heated properly. Place your thermometer in an area where you can easily read it at a glance without it being obstructed by plants or decor.

What to look for in a quality aquarium thermometer


Accuracy is the most critical feature to look for in an aquarium thermometer. Digital thermometers provide the most detailed information, displaying the temperature to a tenth degree. 

Easy to read 

Choose a thermometer that has large, clearly marked numbers. Small text can be challenging to see depending on how large your tank is, and some floating thermometers can be hard to read if they bob on the water’s surface too much.

Simple installation

Select a thermometer that can be easily placed in your aquarium and then relocated without hassle if needed. Thermometers that stick to the glass with an adhesive pad or glue usually can’t be removed without damaging them. 


Some digital thermometers feature an alarm that will beep if the temperature inside your aquarium gets too high or low. This safety feature can prevent the death of your fish in the event of a heater malfunction. 

Cord length

Some digital thermometers plug into a wall outlet for power. Make sure that the cord is long enough to reach your aquarium and still allow the probe to go deep enough into the water to provide an accurate reading. 

How much you can expect to spend on an aquarium thermometer

Depending on the type you choose, quality aquarium thermometers can be purchased for $3 to $25.

Aquarium thermometer FAQ

Will a thermometer harm my fish?

A. Not if used as instructed. Make sure that floating glass thermometers don’t knock against the side of your aquarium. This can cause them to crack and spill fluid into the water. Digital thermometers that get submerged also need to be regularly inspected to ensure there is no battery leakage.

How many thermometers do I need in my aquarium?

A. Most aquariums only require a single thermometer. You can install more than one if you want to know where any especially cold or warm areas are.

Do aquarium thermometers contain mercury?

A. No. Mercury is highly toxic and not used in modern aquarium thermometers. Old thermometers containing silver or white fluid should be disposed of, as this may be mercury.

What’s the best aquarium thermometer to buy?

Top aquarium thermometer

Pets-Best Aquaneat Digital Aquarium Thermometer Set

Aquaneat Digital Aquarium Thermometer Set

What you need to know: For those with more than one aquarium, this set includes three digital thermometers for a great price.

What you’ll love: These thermometers feature a large LCD. They come with batteries installed and also include three spares. You can choose Fahrenheit or Celsius with the flip of a switch.

What you should consider: Some users have noticed inconsistent readings during side-by-side tests of these thermometers.

Where to buy: Sold by Amazon

Top aquarium thermometer for the money

Pets-Best JW Aquarium SmartTemp Thermometer

JW Aquarium SmartTemp Thermometer

What you need to know: Simple and accurate, this thermometer is popular among hobbyists and professional aquarium keepers alike.

What you’ll love: This thermometer stays put using a magnet placed on the outside of the tank. Its numbers and lines are clearly marked, and its red fluid contrasts with its white plastic to make reading it a breeze.

What you should consider: This thermometer sinks if the magnet holding it in place is removed.

Where to buy: Sold by Amazon

Worth checking out

Pets-Best Marina Floating Thermometer

Marina Floating Thermometer

What you need to know: This thermometer sticks to the interior of your aquarium with a suction cup.

What you’ll love: Thanks to this thermometer’s safety zone indicator, you can quickly check to see if your pets are at the proper temperature. It floats in a vertical position and is small enough for betta tanks.

What you should consider: Buyers note that this thermometer’s suction cup is too weak to withstand abuse by turtles or large fish.

Where to buy: Sold by Amazon

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Derek Walborn writes for BestReviews. BestReviews has helped millions of consumers simplify their purchasing decisions, saving them time and money.


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