How to Read a Fish Tank Thermometer Properly

We understand why many beginner aquarists want to learn how to read a fish tank thermometer. After all, water temperature is one of the most vital water quality parameters to ensure your fish is in a safe environment.

If you know how to read an ordinary mercury thermometer, you already know how to read an aquarium thermometer. The process is similar, although the interpretation might be different.

No worries, because we will teach you how to install an aquarium water temperature-reading strip, read a stick on thermometer, and interpret the results. Let us start.

How Do You Read a Fish Tank Thermometer Strip? (pictures)


What to prepare

The following items are necessary for fish tanks without an aquarium sticker thermometer yet. You can forego these materials if you already have the thermometer.


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  • Lint-free cloth
  • Glass cleaner
  • Old PVC card (i.e., credit or debit card) or any flat and sturdy object


Step 1: Choose a location for the aquarium thermometer.


Decide on the fish tank thermometer strip placement. Most aquarists stick the thermometer strip on the aquarium’s side, near the corner between two adjacent panels.

This location is ideal for optimum thermometer accessibility, as you can read temperature strip on fish tank units without it obstructing the aquascape view.

Step 2: Clean the fish tank’s surface where you will stick the thermometer strip.


Moisten a lint-free cloth with glass cleaner and rub it against the aquarium surface to remove dirt, dust, and other contaminants that might impact the thermometer strip’s adhesion. Then, dry the surface thoroughly.

Step 3: Examine the thermometer strip and read the instructions.


Remove the aquarium from its packaging and inspect it for signs of damage. Ensure the adhesive backing has a plastic protective cover you will peel before installation. However, note that some products, such as the Aqua Culture Digital Thermometer, have a paper backing instead of plastic. 

Step 4: Install the aquarium thermometer strip.


Ensure the fish tank surface is free of dirt and other contaminants before you stick the aquarium thermometer strip. You can use the straight edge of a PVC card to press down on the strip to remove any air bubbles.

Ensure the thermometer strip adheres to the aquarium surface. You can wait about 20 to 30 minutes before you read temperature strip on fish tank.

Step 5: Read and interpret the water temperature results


You are now ready to check fish tank temperature. We recommend reviewing the manufacturer’s instructions on interpreting the results.

Some aquarium thermometers are like old-fashioned mercury thermometers. They feature a red line that goes up and down to reflect water temperature fluctuations.

The Top Fin thermometer instructions, for example, are one notable example. Just pay attention to where the red line rises, and compare it against the nearest temperature markings.

Some aquarium thermometers feature color strips for temperature readings. Some products might include an aquarium fish temperature chart to help with interpretation.

So, here is how you interpret or read a strip thermometer. You can rely on the explanation below to read Imagitarium Aquarium Strip Thermometer and other products that feature thermochromic (color-changing and heat-sensitive) liquid crystals:

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  • Green = actual water temperature
  • Blue = decreasing temperature
  • Brown = rising temperature


If you see GREEN and BLUE on the strip, whatever temperature value the green strip is in, it is the current water temperature, but it’s decreasing.

Likewise, if BROWN and GREEN are visible, the green-marked temperature level is the current value. But, the aquarium water temperature is also increasing.

In some cases, the GREEN will not appear at all – the only two colors you’ll see are BLUE and BROWN. When such a thing happens, calculate the average temperatures of these two strips. For example, the real-time aquarium temperature is 78 if blue is 77 and brown is 79.

What about when all three colors appear? In this case, you can ignore BLUE and BROWN, as only the GREEN already shows the right water temperature.

To see for yourself how the process goes, you can check out this tutorial video.

Pros and Cons of a Strip Thermometer

Aquarium strip thermometers are effortless to install and do not cost a fortune.

The principal issue with strip thermometers is their accuracy. These products stick to the aquarium’s exterior wall, opposite the side in contact with the water. Hence, the thermometer not only “senses” the tank temperature but also the ambient room temperature.

There are several solutions to improve a strip thermometer’s accuracy. Placing the aquarium away from direct sunlight and other temperature-sensitive areas (i.e., fireplaces and air conditioner vents) can avoid temperature inaccuracies.

The best solution is a combination of an aquarium thermometer strip and an in-tank temperature sensor. You will be glad you have a backup if one is not working.


How do I know the temperature of my fish tank?

You have three options to know your fish tank’s water temperature.

  1. Stick-on thermometers – These are effortless to apply, unbreakable, and allow installation versatility. The only downside is questionable accuracy. Some products are also challenging to read, especially in low-light conditions.
  2. Standing or floating thermometers – Also known as in-tank thermometers, these devices are inexpensive and allow for versatile placements. They are also more accurate than stick-on.
  3. Digital thermometers – The most accurate of the three types, digital thermometers have electrodes in the aquarium for measuring the water temperature. They are straightforward to use, so you won’t have to go through the headache of figuring out how to read them.

How does a fish thermometer work?

Fish thermometers measure water temperature using three different methods.

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  • Stick-on thermometers feature thermochromic (color-changing and heat-sensitive) liquid crystals to represent water temperature levels. The strip’s temperature range changes in color depending on the prevailing water temperature.
  • Floating thermometers feature a colored liquid column to reflect the rise and fall of water temperatures.
  • Digital thermometers have an electronic probe in the aquarium water to measure temperature and display the reading on a digital screen.


What is the normal temperature for a fish tank?

The normal fish tank water temperature depends on the fish type in the aquarium.

For example, tropical fish are happiest and healthiest at water temperatures between 75 and 80 degrees Fahrenheit. Meanwhile, coldwater fish species find water temperatures between 60 and 75 degrees Fahrenheit the optimal range.

If you have a marine aquarium, the ideal water temperature is 78 to 82℉ for tropical saltwater fish and 75 to 78℉ for reef fish.


Learning how to read a fish tank thermometer gives you the confidence to monitor one of your aquarium’s most crucial water parameters. Although a thermometer strip is less accurate than a digital version, you can still rely on it for general temperature monitoring.

The steps for reading the water temperature should be similar to assessing aquarium temperature using a digital probe or a floating thermometer. The only difference is the temperature-measuring tool.