What To Do When Water Evaporates From A Fish Tank

If you’re a fish owner, you’re probably well aware of the importance of keeping your fish tank clean and well-maintained. However, even the most responsible pet owner can experience some unexpected issues, such as water evaporation from a fish tank.

Water evaporation from a fish tank can be caused by various factors, such as high temperatures, poor ventilation, and low humidity. While a certain degree of evaporation is normal, excessive water loss can be harmful to your fish and disrupt the balance of your tank.

In this article, we’ll explore the causes and consequences of water evaporation from a fish tank and provide you with some practical tips on how to prevent and address this issue.

What To Do When Water Evaporates From A Fish Tank

What is Evaporation?

Evaporation is the process by which water changes from a liquid to a gas. In aquariums, water is lost to the air through evaporation and must be replaced to maintain the proper water level. This process is influenced by several factors, including the surface area of the water, temperature, humidity, and air movement.

Monitoring the water level in your tank is crucial to maintaining a healthy environment for your fish and other aquatic life. By understanding the factors that affect evaporation, you can ensure that your tank remains balanced and healthy. Regularly adding water back to the tank can help compensate for the water lost to evaporation and keep your fish happy and healthy.

Why Does the Water Evaporate So Fast?

Evaporation is a natural occurrence in fish tanks, but the amount can vary depending on your setup. A proper setup should only result in a small amount of evaporation, while excessive evaporation may indicate a problem.

The sun draws water out of the ocean in the earth’s water cycle, and in a fish tank, heat sources cause water to evaporate. Unfortunately, evaporated water from a tank does not return to the tank like in nature.

Proper heat settings are crucial when setting up a fish tank to prevent evaporation and maintain the health of the fish. Water that is too hot can be fatal to your fish, and the excessive heat can cause more evaporation if you do not have a full cover on your tank.

Warm Water

If you have noticed that the water level in your fish tank has decreased, it is likely due to evaporation. The main cause of evaporation is heat, as water molecules become more energized and transform from liquid to gas as the temperature rises.

This process occurs more quickly in warmer water, so it is important to monitor the temperature in your tank and adjust it if necessary. Additionally, be sure to regularly check the water level in your tank and top it off as needed to maintain a healthy environment for your fish.

Lack of Humidity

Evaporation in an aquarium can be affected by a variety of factors, including humidity and temperature. If the air outside of the tank is dry, evaporation will occur more quickly as the air is further from saturation. Similarly, warm air can hold a higher concentration of water vapor, leading to increased evaporation.

This means that evaporation may occur faster in the summer when it is warm, but it can also be affected by dry conditions regardless of the season. It is important to monitor evaporation levels in your aquarium and make adjustments as necessary to maintain proper water levels.

Air Movement

The rate of evaporation in aquariums is influenced by the speed of airflow over the water’s surface. The airflow over a surface causes the removal of water vapor, resulting in decreased humidity and easier water evaporation. Fans can be used to enhance evaporation rates in aquariums by cooling the water surface.

Moving Water Surface

Water agitation can have an impact on the rate of evaporation in your aquarium. When water is agitated, such as through the use of air stones or Gyre pumps, it can cause a larger surface area, which can speed up the evaporation process.

This can result in larger amounts of water leaving your aquarium. It is important to monitor the water level in your tank and make adjustments as necessary to ensure that your fish and plants have a healthy environment to thrive in.

Why is Some Evaporation so Bad?

If not taken care of, evaporation in a fish tank can be fatal for the fish. The process of water evaporation can result in the accumulation of nitrate and ammonia particles, which can be harmful to fish if present in excessive levels.

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While topping off the tank with more water might seem like a quick fix, it can actually lead to stronger ammonia and nitrate levels if done repeatedly. Topping off should only be used as a temporary solution while you address the underlying issue, such as changing the water and ensuring your equipment is working properly.

How Much Evaporation Is Normal for A Fish Tank?

The rate at which your tank water evaporates can vary depending on a number of factors. These include the size of your aquarium, water conditions, room temperature, and the season.

For a standard 50-gallon saltwater tank, you can expect to lose approximately ½ gallon of water per day, meaning you’ll need to add 3.5 gallons of purified water each week. For a 50-gallon freshwater aquarium, the rate of evaporation is slightly higher at around 1 gallon per day.

It’s important to monitor your tank’s water levels regularly and add water as needed to maintain a stable environment for your fish. It should be noted that the evaporation rate of saltwater tanks is typically slower than that of freshwater tanks, as a result of the energy necessary to separate the dissolved salt ions.

How To Add More Water To A Fish Tank

Replacing evaporated water in your aquarium is important for maintaining a healthy environment for your fish. However, simply adding water to the tank can be harmful if done incorrectly.


Proper water conditions are crucial for the health of your fish. When topping up your tank, it is important to use pure, demineralized water to avoid introducing harmful chemicals. If you do not have access to pure water, tap water can be made safe by storing it at room temperature for a couple of days before adding it to the tank.

This will help prevent sudden temperature fluctuations that can stress your fish. By taking these simple steps, you can help keep your fish healthy and happy.


A semi-automated dosing pump can assist with maintaining consistent water levels in your tank if you experience difficulty. The purpose of these devices is to pump small quantities of water into the tank, thereby preventing the water levels from decreasing excessively.

One of the main benefits of using a dosing pump is that it can help prevent mistakes and ensure that you don’t forget to top up your tank. Consider investing in a dosing pump if you want to simplify the process of maintaining your tank’s water levels.

How To Stop Aquarium Evaporation

There are a few ways to reduce aquarium evaporation and maintain stable water levels in your tank. The most important step is to ensure that all of your aquarium equipment is operating correctly and that there are no leaks or other issues causing the water to evaporate.

Regulate Water Temperature

Maintaining the proper water temperature is crucial for the health and well-being of your fish. Fish are unable to regulate their body temperature and rely on the water being in the right conditions to survive. If the water temperature is too high, it can cause evaporation and speed up your fish’s metabolism, leading to harmful toxins in the tank.

Tropical fish species can tolerate a small range of temperatures, so it’s important to keep the water at the cooler end to prevent evaporation. Additionally, fish can become stressed if the water is too warm, so it’s essential to monitor the temperature regularly to ensure it doesn’t rise unexpectedly. This will not only increase the amount of water that evaporates but could also have negative effects on your fish’s health.

Maintain Room Temperature

If you’re struggling with excessive evaporation in your fish tank, there are a few steps you can take to address the issue. One of the most important things you can do is to keep the room where your aquarium is located as cool as possible without being too cold. This can help slow down the rate of evaporation, making it easier to maintain a consistent water level.

In addition to keeping the room cool, it’s also important to maintain humidity in the air. Dry air can speed up the process of evaporation, so adding a humidifier or otherwise increasing the moisture content in the room can help slow down the process.

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Use A Lid

If you are looking for ways to reduce evaporation in your aquarium, adding a glass lid can be a great solution. This can help slow down the rate of evaporation by preventing water from escaping and allowing any condensation to drip back into the tank.

Additionally, a lid can help maintain the water temperature, prevent fish from jumping out, and keep unwanted items from falling into the tank. If your tank doesn’t come with a lid, it can be purchased affordably.

Choose Your Fish Wisely

When choosing fish for your aquarium, it’s important to consider more than just their appearance. For those living in warm, dry climates, it’s best to select fish that can tolerate cooler waters. Some great options include goldfish, bloodfin tetras, rosy barbs, Buenos Aires tetras, pearl danios, and zebra danios.

These fish have the ability to thrive in temperatures that range from the mid-60s Fahrenheit, which means you can maintain the temperature of your aquarium at room temperature without causing any harm to your fish. By selecting fish that are well-suited to your environment, you can create a healthy and thriving aquatic community.

Change The Water Filter

If you are experiencing evaporation problems in your fish tank, your filter may be the culprit. Old or clogged-up filters can malfunction and overheat, causing the water to warm up and evaporate at a faster rate. This can also be dangerous for your fish if they get too close and risk being burned.

If cleaning the filter does not solve the problem, consider investing in a new and more efficient one to see if it helps reduce evaporation.

Turn Off The Lights

Excess heat from aquarium lights can cause evaporation, so it’s important to take steps to minimize this. One solution is to turn off all lights at night, which not only helps with evaporation but also allows your fish to get a good night’s sleep. Fish are diurnal and sleep at night when it’s dark. In the morning, you can turn the lights back on.

If your lights generate excessive heat during the day, consider switching to high-efficiency, low-energy bulbs that provide enough light without giving off too much heat. If you use your lighting system to heat the tank, remember to turn down the heater to conserve electricity. It’s important to ensure that any changes you make to your lighting system are safe for your fish and do not affect the water chemistry of your tank.

Test The Water

Maintaining the appropriate water temperature in your fish tank is important for the health and well-being of your fish. However, it can be difficult to monitor the temperature by eye alone, as sudden rises can occur without warning. To maintain a stable water temperature and prevent excessive evaporation, it is advised to regularly check the temperature with a reliable thermometer.

There are different types of thermometers for aquariums, including clip-on and probe models. The most precise ones are those with a probe that can measure the temperature of the water. Thermometers equipped with a probe are considered to be more precise as they allow for direct testing of the water, rather than just the container.

When choosing a thermometer, select one that will encourage you to stick to a regular temperature-taking routine. This will help ensure that your fish are kept healthy and comfortable in their environment.

Reduce Your Tank Size

If you’re experiencing excessive evaporation in your fish tank, it may be due to the size of the tank. Tanks with greater width possess a greater surface area, consequently leading to increased evaporation. This can lead to a dwindling water supply and potential harm to your fish if harmful ammonia and nitrites rise.

Consider switching to a smaller tank and reducing the number of fish you have if the evaporation is causing problems. Topping up the water every day is not a long-term solution. When considering changes to your tank, it’s important to take into account the potentially time-consuming process of dealing with evaporation and whether the tank size is appropriate.

Is It Necessary To Replace Evaporated Water In a Fish Tank?

Evaporating water in your fish tank can have a significant impact on the balance of your aquarium. As water contains salt and minerals, evaporated water becomes denser with these elements, which can be harmful to your fish and the mini-ecosystem of your tank. Maintaining proper levels of water in your fish tank is crucial to avoid any potential harm to your aquatic pets.

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Failure to do so can change the nutrition level, pH, water, and salt level/salinity, ultimately affecting the lives of your aquatic residents and the ecological balance of your tank. Be sure to monitor and maintain the water level in your fish tank regularly to ensure a healthy environment for your fish.

Problems Caused by Water Tank Evaporation

Water tank evaporation can have a detrimental effect on the health and well-being of your aquatic inhabitants. When water evaporates from an aquarium, it leaves behind impurities such as minerals and salts which can change the water’s chemistry and become toxic to fish.

Rising Ammonia Levels

Evaporation can lead to an increase in ammonia levels in your fish tank, which can be harmful to your fish. Fish are sensitive to ammonia and prolonged exposure can lead to poisoning and burns. It is important to monitor the water quality regularly and perform water changes to prevent the build-up of harmful toxins.

Signs of high ammonia levels include foul odor, fish gasping at the surface, motionless fish, loss of appetite, and redness around the gills. Regular water changes can help maintain a healthy environment for your fish.

Increased Salinity

Maintaining the proper salinity levels in a saltwater tank is crucial for the health of your fish. As water evaporates from the tank, salts, and minerals are left behind, causing the salinity levels to increase. This can lead to dehydration and slime on the fish’s scales, and in severe cases, death.

To prevent this, it is important to regularly top off the tank with fresh water. Automatic top-off systems can be particularly helpful in maintaining consistent salinity levels in saltwater tanks. By keeping the salinity levels stable, you can ensure the health and well-being of your fish.

Low Oxygen Levels

Maintaining proper oxygen levels in your fish tank is crucial for the health and well-being of your fish. Evaporation can lower the tank’s oxygen levels, which can lead to a variety of symptoms. These symptoms include fish gasping at the surface for air, lethargic and non-moving fish, lack of appetite, and labored breathing, which is seen through the rapid opening and closing of the gills.

To prevent these symptoms, you can add more water to the tank or increase the number of plants and suitable substrate. Decreasing the number of fish can also help. Expanding the surface area and aeration of the aquarium can enhance oxygenation, but it can also accelerate the process of evaporation.

It is important to monitor the oxygen levels in your tank and take action if you notice any of these symptoms. By maintaining proper oxygen levels, you can help ensure the health and happiness of your fish.

Stressed Fish

It is important to keep your fish’s environment stable to prevent stress and illness. Even minor changes, such as evaporation, can cause overcrowding and lead to symptoms of stress, including increased aggression, frantic swimming, and hiding away.

Additionally, improper water conditions can exacerbate stress, so it is important to maintain proper salt levels, ammonia levels, and pH levels. To prevent evaporation from causing issues, it is important to regularly top up the water in your tank.

By providing stable and optimal conditions, you can help keep your fish happy and healthy.


The evaporation of water from your fish tank is a common occurrence that can be easily managed if you take the necessary steps. Regularly monitoring the water level, topping up the tank with fresh water, and checking the water parameters are crucial to maintaining a healthy environment for your fish.

It’s also important to keep in mind that evaporation can be influenced by factors such as temperature, humidity, and air circulation. By understanding the causes and taking preventive measures, you can ensure that your fish tank remains a safe and comfortable home for your aquatic pets.