Is Condensation In Your Fish Tank Heater Normal? What You Should Do About It!

Estimated read time 5 min read

Is finding water, bubbles, or condensation inside your aquarium heater normal? Is it bad, and what should you do if it happens to your heater?

Water can get into an aquarium heater in a few different ways, especially if the glass has cracked.

While condensation in a fish tank heater is normal for some heaters, it can also be a sign of a problem.

If you see condensation inside aquarium heater parts, it might be an indicator that something needs to be fixed or replaced.

If you notice that the inside of your fish tank heater looks foggy or moist all of a sudden!

Then keep reading to learn everything you need to know about condensation and fish tank heaters.

Related: How To Use Aquarium Heater

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How Does Water Get Into Your Fish Tank Heater?

Below are a few ways water can get into your fish tank heater or possibly cause condensation to form:

Glass Is Cracked

If your aquarium heater’s glass tube becomes cracked, water can rush into the submerged heater.

Even if the crack is tiny and thin, moisture can find its way into the fish tank heater.

This can fry the electrical components and the water in your aquarium.

Seal Is Broken

Moisture can also seep into your heater if the seal is broken.

The seal is usually a rubber piece at the top, and it can become worn out and damaged over time.

Once water gets in, it makes the seal pointless since it’s meant to protect the delicate electrical components.

Humidity During Manufacturing Process

Although cracked glass and broken seals are an issue, it is normal for some aquarium heaters to have condensation inside, which most manufacturers will note on their websites.

When heaters are exposed to humidity while being made, condensation will appear in the glass tube simply due to differences in the tube’s temperature and the water outside.

If you only notice condensation, it’s not enough water to cause problems, so you don’t need to worry.

How Can You Tell If Your Fish Tank Heater Has Water In It?

Below are a few ways to tell if your heater has water in it:


If you see bubbles moving around inside the glass tube, this is a sign that a decent amount of water has likely entered the heater from damage to the glass or the seal.

Moisture or Water

If there appears to be a lot of liquid moving inside the tube, it is a sign that there is too much water entering the heater.

This much moisture might actually cause dark spots to appear on the glass from the internal parts frying.


If you are only seeing the fog of condensation and no bubbles or fluid moving around in the tube, it is probably just the normal condensation, possibly from the assembly.

However, seeing all three is a bad sign.

Is Water Inside Your Fish Tank Heater Bad?

If you see water inside your heater, it is a bad sign.

Any water that can get into your fish tank heater can cause damage to the delicate electrical components that should never come into contact with water.

Failing to prevent this could cause your fish tank heater to catch on fire.

Are Bubbles On Your Fish Tank Heater Also A Bad Thing?

In contrast, it is normal for bubbles to form on the outside of your heater after it has been running for quite some time.

As the water around the heater gets hot, it will hold onto less air, which is then released into bubbles that will eventually rise to the top of the aquarium.

If you see bubbles, don’t worry, be happy.

What Should You Do If You Have Water In Your Fish Tank Heater?

If you have water inside your fish tank heater, the following options are available to you:

Try Fixing It

You can try to replace the damaged glass tube or seal and take the heater apart to let it dry, although most people find that this process is too time-consuming to be a good option.

However, if you have the patience to fix your fish tank heater, this option is typically a bit cheaper.

Replace the Heater (Recommended)

You can also replace the fish tank heater with one that may be less likely to develop internal water damage.

Then ensure that your heater is installed correctly and make sure you know if it’s a submersible heater?

Video: Aquarium Heater Condensation – Is It Broken?

Key Takeaways

When it comes to your heater, you need to be careful. Any powered piece of equipment poses a threat of fire if you don’t take care of it.

If you notice any of the following;

  • Water
  • Bubbles
  • Cracks or Broken Seals

You should immediately turn off your heater and replace it as soon as possible.

In fact, it’s always a good idea to have a backup heater just in case your heater stops working or shows signs of water infiltration.

With that said, click here to see the aquarium heaters we recommend the most.

Tank on.


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