Do Aquarium Thermometers Contain Mercury? (How To Find Out?)

Image of an aquarium thermometer without mercury

Aquarium thermometers don’t contain mercury. Mercury is highly toxic and no longer used in aquarium thermometers. To find out if a thermometer contains mercury, check the color of the substance inside the thermometer. If the color is silver-white to gray, then the thermometer is filled with mercury.

Let’s take a deeper look at this now.

4 Types Of Aquarium Thermometers

The temperature inside the aquarium is an essential parameter for aquatic pets and plants to flourish.

So it’s necessary to have a quality thermometer to check the water temperature.

Given below are the different types of aquarium thermometers used in aquariums.

1. Strip Thermometers

Strip thermometer

Strip thermometers are also known as Sticker thermometers. They are inexpensive and straightforward to use.

Since the temperature reading is provided by the changing color of the liquid crystal ink, they are also known as Liquid Crystal Displays (LCDs).

However, don’t mistake them for digital aquarium thermometers.

They can be installed very quickly on the outside of the tank. You can start with wiping the exterior glass of your tank.

Next, peel the strip on the thermometer’s backside that has an adhesive and press it against the glass wall.

Strip thermometers are not the most accurate thermometers because they’re designed to be mounted on the exterior side of an aquarium; the outdoor temperature affects their accuracy.

So although they are inexpensive and easy to use, they are not accurate and reliable.

2. Glass Thermometers

Glass thermometer

These are the most common type of aquarium thermometers.

Glass thermometers have an old design but are versatile and reliable in measuring water temperature.

Moreover, glass thermometers are placed inside the aquarium, which helps to measure the temperature accurately.

They are also inexpensive and therefore preferred by many aquarists.

These thermometers are handy as they provide accurate readings and are also easy to read and use.

Given below are the different ways to install a glass thermometer in your aquarium.

i. Floating

A floating thermometer measures the water temperature by attaching itself to an object that floats freely in the water.

It will let you install the temperature sensor at any depth without having to worry about whether there’s enough room for the probe.

Remember that most glass thermometers are used by themselves; however, they need an appropriate attachment if you want them to float upright.

The downside of a floating thermometer is that it can get pushed to the rear end and pose a challenge to read the temperature reading.

Moreover, it can easily get damaged due to continuous collision with other objects.

ii. Standing

A glass thermometer with a weighted base makes it an excellent standing thermometer.

You can install it at any point where there’s enough space without interfering with the water flow.

However, a standing thermometer isn’t helpful when the aquarium glass has curves.

In such cases, installing the thermometer is difficult because there might not be enough space between the glass and the thermometer.

The challenge with a standing thermometer is that it can easily get pushed around by large fish.

So you must find a place in the aquarium to ensure that your thermometer stays upright.

iii. Submerged

A glass thermometer can also be used as a submersible thermometer, which means the thermometer is submerged under the water.

To submerge the thermometer, you can attach a suction cup to the glass thermometer.

So it can be easily used as a submersible temperature gauge.

Moreover, it’s easy to move the thermometer around as per your needs.

But it’s best to have a fixed position, making it easier to read the measurement and handle the thermometer.

3. Digital Thermometers

These thermometers use a digital display to show the current temperature.

They are generally more expensive than other thermometers but provide a more accurate reading of up to 0.1°F than analog thermometers.

A digital thermometer consists of a probe inserted in the aquarium water, either permanently or just for one reading.

The probe connects to a digital display located outside the aquarium.

Some models use wireless technology for their probes, while others need an actual physical connection between the device and the monitor.

Usually, the sensor probe is connected directly to the screen, so there’s no need for an additional attachment point.

Most models need batteries to run, but some high-end models can be plugged directly into an electrical socket.

In addition, some models place both the sensor and display within the tank.

However, there’s a risk of battery leakage. So a display outside the tank is a safer option.

Moreover, some high-end digital thermometers also provide an audible alert feature.

They sound an alarm when the temperature is outside the required range.

4. Digital Laser Infrared Thermometers

A digital laser infrared thermometer is a handheld device and not installed inside the tank.

You can point this thermometer at the aquarium water to measure its temperature.

However, you can’t use it as a primary thermometer.

Instead, use it as a secondary thermometer to measure the temperature during a water change.

For example, you can use this thermometer during regular maintenance activities like changing the tank water.

You can check the water temperature before adding the water to the fish tank.

How To Find Out If A Thermometer Contains Mercury?

Mercury is a silvery-white to grayish substance.

So if your thermometer contains the silver-white to gray substance, then your thermometer is filled with mercury.

On the other hand, if your thermometer contains red liquid, it’s the red-dyed alcohol or mineral spirits.

So you can safely assume it’s not mercury. Such thermometers are a safer alternative to mercury thermometers.

You must always use caution while handling a mercury thermometer because any accidental damage can result in mercury spills which can have dire consequences.


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