do fish tanks increase humidity?

Do Fish Tanks Cause Humidity?

Fish tanks contain water, and with water comes the talk of evaporation and condensation and questions of whether these processes can affect the relative humidity of the home.

Tropical fish tanks will produce excess moisture due to evaporating water. This will increase humidity in the room it is in.

In this article, we will be answering some frequently asked questions on whether or not fish tanks can impact humidity.

What is Humidity?

Humidity is the presence of water vapour in the air. Basically, the more water evaporates within an area, the more water vapour rises into the air, and that’ll cause the humidity of that area to increase.
For homes, humidity is quantified by relative humidity (RH). The relative humidity is a measure of the water vapor content of the air. The amount of water vapour present in the air is presented as a percentage (%RH) of the amount needed to attain saturation at the same temperature.
RH is directly proportional to temperature and highly sensitive to temperature swings. This means that for a system with a stable temperature, the RH will also be stable. Relative humidity also depends on the system’s pressure just as much as it depends on the temperature.
As a general rule of thumb, the air becomes drier (RH decreases) as temperatures increase, and as temperatures decrease, the air becomes wetter (RH increases). Regarding pressure, you should also bear in mind that the air becomes drier (RH decreases) as pressure decreases, and as pressure increases, the air becomes wetter (RH increases).

Following so far? Good!

Humidity is essential, and we should pay attention to the relative humidity of our homes for
several reasons:
● Humidity can affect the quality of some finished products like chocolate where it can cause discoloration of the bars. I have only recently found this out, and have always wondered why sometimes a chocolate bar is a funny colour.
● Humidity can also have an expensive impact on products such as building materials like cement. Imagine laying a concrete subfloor before putting down hardwood flooring. If the concrete isn’t sufficiently dry before you lay the floor, the consequences can be severe as any moisture from the concrete will naturally try to migrate to a drier area, causing the floor to swell, blister, or crack. This can undo all your hard work and force you to replace the floor completely.
● For products with extreme sensitivity to moisture, humidity can be devastating, such as certain pharmaceuticals. Moisture can alter the characteristics of the product until it becomes useless. This would explain why products like medical pills and dry powders should be stored in controlled conditions at precise humidity and temperature values.

Will a Fish Tank Increase Humidity?

humidity with a fish tank

Yes, fish tanks will increase indoor humidity. You could even say an aquarium is one way to increase your indoor humidity naturally without using a humidifier.
The indoor humidity in your home can be increased with fish tanks through evaporation. When the heat tank is subjected to even minimal heat levels in the air, evaporation naturally occurs. This evaporation keeps the room humidified. In some cases, it may be so severe that you’d need to get a dehumidifier for the same room that has the fish tank.
If you live in an area characterized by dry air, like Nevada, then you’d be grateful for having an aquarium in your room.

But it’s not all bad news.

An aquarium will increase the humidity in the air and help ensure a night of better sleep for you.
Evaporation is part of the cycle of a fish aquarium. If you were to close the windows to keep the dry air outside, the aquarium might be enough. And if you’ve got a giant aquarium, you can even open the doorways so that the same vapour can creep into other rooms.
Some people report an average of about 2 inches of water is evaporated from their fish tanks a week, with evaporations rates getting as high as 5 inches in a week in the summer. This only goes to reveal that fish tanks can increase the amount of humidity in a room.

I personally have to top my water up at least twice a week due to this, especially when it is warmer weather.

Will a Dehumidifier Take Water out of a Fish Tank?

do fish tanks increase humidity
A dehumidifier

Running a dehumidifier can take out water from a fish tank as it will increase evaporation in the room.
A dehumidifier works a bit like a vacuum cleaner: it sucks in air from your room at one end, sips out the moisture from it, and then blows back the now-dry air out into the room again.

The extracted moisture drips through the dehumidifier into a collection tank that’ll need to be emptied from time to time. This leaves the air in the room dry and sometimes warmer.

If there’s a fish tank in the room, then the rate of evaporation will increase to attain some level of equilibrium in the moisture content of the air and the fish tank. And as more air is stripped of moisture, more keeps escaping to the surrounding air, thereby draining the fish tank of water. The result would be decreased levels in the fish tank with time, so you will need to ensure you regularly top up your tank water.

Is Condensation in a Fish Tank Bad?

Well, it depends. Typically, where there is water, you can expect there to be evaporation taking place. While condensation is a natural process in the aquarium life cycle, it can cause your hood lighting system issues. All that moisture lingering around the lights can cause a short-circuit with the potential for fires erupting. But this is in very extreme cases.

It is worthy of note that you shouldn’t mistake air pump bubble condensation for regular fish tank condensation. Your air pump can cause bubbles to break on the surface of the water and cause splashes on the aquarium hood. Eventually, condensation would build, and dripping would occur. Heat condensation occurs when warm evaporated water collects on cooler surfaces and
returns to its former liquid state. If you don’t have an air pump, but you still experience condensation, then regular heat condensation is the likely culprit.

How to Stop Condensation in a Fish Tank Hood.

condensation on a fish tank hood
Condensation on a fish tank hood.

Even though condensation occurs somewhat naturally, there are still strategies you can apply to mitigate its impact on your fish tank
● Drill holes on the fish tank hood to reduce the amount of water vapor build-up on the lid. While this will allow some of the water to escape, thereby slowly reducing the water content of your tank, it would work if the condensation situation is complex.
● Try tilting your fish tank so that water vapor that collects on the lid would slide off and fall back into the tank. But be careful. Altering the balance of the tank can create new problems for your tank and even prematurely age the tank, weakening the adhesive on the tank panels.
● You could also go old school by purchasing condensation trays. These are clear plastic ribbed lids that go on top of the tank under the lights to stop the water from reaching them. These would ensure you don’t get any electrical issues due to the water vapor.
● Raise the temperature of the tank hood, so it goes beyond the core temperature of the fish tank. That’ll ensure water vapor doesn’t stick to the hood. You could do this by placing towels on the top.

I have a rolled up towel on the floor behind my fish tank so when I open my tank, any condensation that drips off the lid and goes down the back of the tank will be caught by the towel.

Can Fish Tanks Cause Mould?

Yes, fish tanks can cause mould.

As explained earlier, fish tanks can increase the level of humidity in a room. That means if evaporation is constrained to a single room, then you can easily see the humidity levels in that room rise to 80% or even more. This could cause the spread of mould under or behind things, in the dark corners of the room, and so on.
You could even have a home that seems utterly free of mould, but once an aquarium gets added to the mix, the moisture levels of the house will increase, and mould could begin to show.

Now, this is not to imply that mould would spontaneously start to grow with the introduction of a fish tank, but the addition of an aquarium could set conditions suitable for the proliferation of mould if the additional moisture ingress isn’t adequately accounted for and handled.
Mould usually grows on walls, floors, carpets, furniture, appliances, as well as anything that can provide a surface and food to sustain its growth. Most homeowners would typically find mould in some common areas like the kitchens, bathrooms, attics, windows, and basements, as these areas are usually exposed to a great deal of moisture. Also, areas with poor or low ventilation
may easily get hit with an excess humidity problem.

Generally, the signs of mould growth to look out for include:
● Cracked paint
● Discoloration on walls
● Surfaces and fabrics feel damp
● Wall surfaces becoming soft
● Warped flooring
● Musty odours

While mould may not be lethal, it can become dangerous when left unattended to and allowed to grow to large volumes. It can:
● Destroy Fabrics: Mould can cause damage to your clothes, furniture, and any other fabric item that it is allowed to grow on
● Destroy Wood: Mould can induce dry rot to wood structures, and that can be a costly problem to fix.
● Destroy Carpeting: In some cases, moulding may warrant a complete replacement of carpeting, which can be expensive.
● Cause Bad Odour: Mould can cause a foul odour that can sometimes be impossible to remove altogether.
● Cause allergies: Mould can produce Mycotoxins in the lungs when inhaled, causing allergic reactions like stuffy nose, red or itchy eyes and skin, wheezing.

Related Articles:

Can Tropical Fish Survive Without a Heater?

Why does the Water Level in my Fish Tank go Down?

Why do I have GREEN fish tank water?

How often should I clean my fish tank filter?


Fish tanks can cause humidity due the excess moisture in the air produced by the tank. There are, however, ways to minimise it, and things to look out for to prevent mould starting to form in your property.