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A Guide to Fish Tank Thermometers

For anyone who has led a very sheltered life, a thermometer is a tool that measures the temperature of things.

We stick them into sick children and into sponge cakes.

We also need them for our aquariums!

A thermometer for your tropical fish tank is an absolute must.

happy fish
This fish is happy, but is he warm enough??

If you keep tropical fish you need a heater to keep the water temperature at the correct level for your fish. It is impossible to know the temperature in your tank just by looking, so a thermometer is essential to monitor the temperature in your aquarium.

An aquarium thermometer is an essential piece of kit for your tropical fish tank, and there are plenty available to choose from.

fish tank thermometer

Different Types of Thermometers.

There are 4 main types of aquarium thermometers to choose from:

Stick on LCD (Liquid Crystal Display) Thermometers.

This type of thermometer usually comes as part of an aquarium starter kit.

This thermometer sticks onto the outside of the fish tank.

There is always debate as to how accurate this type of thermometer is, mainly because it measures the temperature from outside of the tank. Factors like room temperature and the thickness of the tank could affect the accuracy.

If you have a large tank, it is best to have a few stuck to your tank, as it will be easier to spot a problem area. However, a downside to this is unsightly black strips blocking your view of the fish!

You should never have the thermometer in direct sunlight or near to a radiator. This should never happen though as we all know not to put a fish tank in direct sunlight or near to a radiator, right?

This pack of 10 stick on aquarium thermometers are good value. They have 3 different coloured markings on them so you can easily monitor if the temperature is in the permitted range.

Floating Thermometers.

The term ‘floating thermometer’ is a little bit misleading as most of them are weighted underneath to anchor them to the bottom of the tank. They don’t usually bob around the tank with the fish, although a few of them do!

These tend to be more accurate as they are inside the tank.

They are not the best choice if you have boisterous fish as it can be knocked and bashed about a bit. If a boisterous fish knocks it about to much it will start creating a lot of movement in the water which could then stress your other fish out.

The majority of them are made out of glass so are therefore breakable.

They can also be harder to read, depending on where you have put it in the tank. If it is at the back so it is out of the way, you may have to wait until there are no fish swimming in front of it to see a proper reading. However, the ones that bob up and down in your tank will move around, which I know I would find annoying!

This floating thermometer is made out of plastic rather than glass which makes it safer to put into your tank.

Standing Thermometers.

Standing thermometers tend to have a suction cup that you attach to the inside of the tank. You can also get ones that have a clip that attaches over the side of the tank.

These thermometers aren’t digital, but they are fairly easy to read as they usually have a ‘safe zone’ marked out in a different colour.

This is the thermometer that I use in my tank. It sticks to the inside of the tank with a suction cup, and is very accurate.

I use this one as my water heater has a digital thermometer, so this standing thermometer is my back up.

Digital Thermometers.

Digital thermometers are usually the most accurate.

A digital thermometer consists of a probe and a little digital display monitor.

Depending on what type you buy, and there are a wide range to choose from, some have the digital display under the water with the probe, whilst others sit outside of the tank.

The main advantage of the display being out of the water is that there is no danger of the battery leaking in the tank, which would be fatal.

The pricier versions you plug into a socket, which stops any battery issues but you need a spare socket which is always a rare phenomenon for an aquarist!

Some digital thermometers will sound a warning alarm if the temperature goes out of the desired range.

An important thing to check if buying this type of thermometer is how long the cord is between the probe and the digital display. Some cords can be quite short which makes it difficult when finding somewhere outside of the tank to stand.

If you are buying an electrical thermometer, rather than a battery operated one, check the length of the wire to ensure it reaches your plug socket.

This digital thermometer is one of the top sellers on Amazon. It comes as a 2 pack which is great value.

I like that both the probe and the digital display have suction cups which make it easier to attach to the inside of the tank (for the probe), and outside of the tank (for the display monitor).

Related Articles:

Does tropical fish water feel warm?

Fishkeeping tips for beginners

Can tropical fish survive without a heater?


fish checking out the temperature

Why do you need a thermometer in a fish tank?

It is essential if keeping a tropical or marine aquarium that your temperature stays at a constant level. The temperature is determined by which species of fish you have.

The easiest way to regularly check the temperature is with an aquarium thermometer which is a permanent fixture in or on your tank.

Where do you place a thermometer in a fish tank?

You should never place the thermometer next to your water heater. It needs to be on the opposite side to the heater if possible.

If you have a large aquarium, it is best to have an extra thermometer in a different part of the tank to ensure it’s the correct temperature throughout.

Can you use a regular thermometer in an aquarium?

It is better for an aquarium thermometer to be monitoring the temperature constantly, which is why they are attached onto, or placed inside of the tank.

A regular thermometer is handheld so wouldn’t be suitable, although it wouldn’t be dangerous to the fish if used to take the temperature as a one off.

How do I know if my thermometer is accurate?

The best way to check the accuracy of your thermometer is with an ice test.

Fill a jug full of ice cubes and place the thermometer into it. Move it around for a few seconds and then check what the temperature is. If it reads anything different to 32 degrees Fahrenheit (0 degrees Celsius) it isn’t accurate.

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