How to Stop Condensation Forming on Top of Fish Tank Glass?

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An aquarium lid brings many benefits, but there’s one significant downside to worry about— the dreaded condensation. Water droplets keep forming on the lid, obscuring the view and the light penetration into the aquarium.

Plus, it just doesn’t look good. It becomes annoying having to wipe down the lid constantly. Unfortunately, condensation is to be expected.

It happens due to the high humidity and temperature differences in the tank. When the warm water vapors hit the aquarium lid, the interaction with the cool glass chills the vapors to the water’s dew point. This releases the water in the vapors, causing condensation.

If the lid and the aquarium water have the same temperature, you can’t cool the vapors to the dew point.

You can prevent this process by raising the temperature of the glass. This means the room and aquarium temperature should be kept equal.

Another solution is circulating the air under the lid. You won’t get condensation if you prevent the vapors from reaching the glass lid. However, the second method is harder to put into practice.

Other people recommend using a mesh top instead of a lid. While this stops condensation, it’s not a suitable replacement for a proper lid.

I’ll explain why the lid is essential in further detail. But first, let’s discuss condensation a little further. Is it something to worry about? Keep reading to find out!

Is Condensation Bad for Your Tank?

Condensation takes away from the aquarium’s appearance. Noticing it for the first time might even be distressing.

After all, condensation is the leading cause of mold. But don’t worry! Your aquarium is completely fine. This phenomenon is common and shouldn’t lead to any adverse effects.

There are two things worth mentioning, though:

  • Condensation affects light exposure

Condensation doesn’t directly impact the living things in your tank. But it can make an indirect contribution. Condensation slightly reduces the light penetration into the aquarium. The water droplets on the lid will scatter the light.

This reduces the number of rays traveling directly to the bottom of the tank. You might find plants grow slower than expected due to the lower light exposure if you have plants. However, this small impact shouldn’t otherwise hurt the plants (or fish). 

  • Condensation might sometimes represent a hygiene issue

By itself, condensation is harmless. Well, as long as the aquarium is well maintained, that is. The water quality matters. Remember that condensation happens when water vapors from the tank reach the glass lid.

If your aquarium water is unclean, condensation can become a problem. When the lid gets dirty, this facilitates bacteria and fungus growth.

Why Should You Keep the Lid on Your Tank?

The water droplets forming on the lid aren’t dangerous for your fish. However, getting condensation is still annoying. Sometimes, you want to get rid of the lid altogether.

But you’ll want to reconsider. Tiresome as it is, having an aquarium lid is still very useful. Here are just some of the most important reasons why you need to keep the lid on:

– To Reduce Evaporation

Water is going to evaporate, nevertheless. But the lid slows down the process. This is very helpful because evaporation can increase concentrations of nitrites and nitrates in the tank.

As the water volume decreases, the percentage of waste by-products will rise proportionally. This can mean negative consequences for the water quality and fish.

Coming back to condensation— some of the droplets on the lid will drip back into the aquarium water. So, the water evaporates, the vapors get cooled to the dew point, and the “dew” drips back into the tank.

This is the primary mechanism behind slower evaporation. In turn, you’ll have to top off the water less often and get stabler parameters.

– To Prevent Fish from Jumping

This one is pretty straightforward. Some fish are infamous for their jumping abilities. It would help if you had something to keep them from jumping out of the tank. And an aquarium lid is perfect for that.

Unlike a mesh, the lid is more stable and gives you better visibility inside the aquarium. Both for aesthetic and practical reasons, the lid remains a top choice.

Lids provide more weight and stability to counteract even the strongest jumpers! A mesh might be good enough for smaller species like Guppies, Tetras, or Bettas. But if you keep larger and stronger fish like Clown Loaches or Swordtails, the lid is your friend.

– To Prevent High Humidity in the Room

As you know, high humidity is the leading cause of black mold formation. Typically, you’ll see its effects on ceilings and exterior walls, especially near windows.

Sometimes, you’ll also see this near open aquariums. An aquarium without a lid can significantly impact room humidity levels. This potential problem will be worse in smaller rooms or if you have a large aquarium.

Once again, the lid comes to the rescue! It helps trap the humidity inside the tank, maintaining your room at a healthy and comfortable 30-50% RH.

The lid also prevents the water vapors from traveling to the walls and ceiling in your room, thereby keeping mold formation at bay.

– To Keep a Stable Temperature in the Tank

Maintaining a stable temperature is crucial no matter what fish species you keep. Rapid temperature fluctuations can be stressful and hazardous, even for sturdier species.

You probably already have a bunch of equipment dedicated to this purpose— a water heater, a thermometer, maybe even a chiller.

And the lid can be another critical piece in your arsenal. The lid doesn’t just trap moisture but also heat. It keeps the warm air from circulating outside the aquarium, reducing energy requirements to maintain a stable water temperature.

The lid also acts as a barrier between the aquarium water and the air in the room. It separates the room-temperature air and prevents it from chilling the upper layers of the aquarium.

Even if you get wild variations in room temperature, the lid prevents the aquarium from cooling rapidly.

How to Prevent Condensation from Dripping Out?

Usually, the condensation would stay inside the tank. If the water droplets leak, the lid is either not adequately secured or too large for your aquarium.

The best solution, in this case, is to use a properly-sized lid.

Choose a lid that doesn’t go over the perimeter of the tank. If you use an aquarium hood instead, avoid gaps between the aquarium rim and the hood edges.

Any extra room outside the rim of the aquarium provides extra space where the water can condensate and drip.


Condensation is a natural phenomenon that is normal in covered aquariums. It happens when warm vapors travel from the water to the aquarium lid.

The vapors get chilled to the dew point if the lid is colder than the water temperature. Then, water droplets form on the lid.

This can be upsetting because it takes away from your aquarium’s appearance. But know that condensation isn’t dangerous for your plants or fish.

Even if you get condensation, keeping the lid is better than the alternative. The lid brings multiple benefits, including slower water evaporation, stabler temperature in the aquarium, fish safety, and stabler room humidity.

If you still want to prevent condensation, you have two options. Maintaining the room and aquarium temperature at the same level will prevent vapors from reaching the dew point, thus stopping condensation in its tracks.

You can also circulate the air in the aquarium to prevent the vapors from getting into the glass in the first place.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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