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How to Increase Oxygen in a Freshwater Aquarium: Tank Tips

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Making sure there is enough oxygen in a freshwater aquarium is essential for the quality of life of your fish and other creatures. 

Having a decreased oxygen level can cause a plethora of health and tank issues. 

Increasing oxygen in a freshwater tank can be done by adding live plants, carrying out partial water changes frequently, adding a high-powered filter, or adding a bubbler. You can also add multiple air stones. If you see any signs of a low oxygen level, it is important to take action right away.

Keep reading to learn more about the signs of your freshwater fish tank being low on oxygen, how to increase the oxygen in your tank, and why the oxygen may be low. 

How To Tell If Oxygen Levels Are Low

Aside from testing the water for dissolved oxygen levels in the water. There are several signs that there is not enough oxygen in your tank. 

The behavior changes in your fish are going to indicate there is a problem in your tank. When you notice abnormal behavior in your fish you will need to find the cause. 

Air stone aquarium

This can be done through a test kit for dissolved oxygen levels.

Behavior signs that the oxygen is low in the tank:

  • Less movement: The initial reaction to low oxygen levels is less movement. This includes swimming slower than usual or less. This is because the fish’s energy is used more for breathing than swimming. As the oxygen drops more they will have labored breathing and their gill movements will become more rapid as they try to get some oxygen from the water.
  • Gasping for air: Your fish will eventually start moving toward the surface of the water and will gasp for oxygen. This is often confused for hungry fish wanting to be fed. This behavior is also shown in labyrinth fish, mistaking the gasping for oxygen as regular breathing.
  • Eating less: As the oxygen in the tank drops the fish inside the aquarium will begin to eat less food over time.

How To Increase Oxygen in Tank

There are plenty of different ways to add oxygen back into your tank. Some things you can do is to increase the surface area of the aquarium itself. 

For a quick short-term fix, you can create water movement on the surface. Creating more movement at the surface by increasing the filter system power or even taking a cup and scooping water and dumping it back in from a height.

Although there are quick fixes to help add some oxygen back into the water in case of an emergency. 

There are ways to keep your tank oxygenated, which will avoid future problems of having a low oxygen level. 

Live Plants

Live plants have numerous benefits for aquarium tanks, especially adding oxygen to your tank. 

This is because the plant pulls carbon dioxide from the water that is produced by the fish. They release oxygen back into the water. 

This also helps create natural habitats for fish as well as maintain proper oxygen levels.

Although live plants can occasionally deplete oxygen levels. This is because they are not exposed to light. 

When plants are exposed to light they will absorb the carbon dioxide in the water and release oxygen. When the plant does not receive the light that process actually reverses and they will consume the oxygen instead. 

When placing plants in a tank to add oxygen make sure there is enough light but adding or increasing light levels during the day raises oxygen levels.

There are some plants that are very hardy and grow rapidly. These plants will do well in bringing lox oxygen levels back up to healthy levels. 

Adding live plants to your tank is also a great way to prevent algae growth. As the plant grows it will absorb the nutrients the algae needs right out of the water to prevent growth. 

Preventing the algae growth is also important in maintaining all water parameters including oxygen.

Examples of good live plants to add to your tank:

  • Amazon Sword
  • Hornwort
  • Eelgrass
  • Java Moss
  • Fanwort
  • Java Fern
  • Water Wisteria
  • Dwarf Hair Grass
  • Water Sprite
  • Green Tiger Lotus

Water Changes

Large water changes of about 50% of the water can add plenty of oxygen in case of an emergency. 

This will easily replenish the loss of oxygen in the water. However significant water changes can create stress on the fish, especially with the pressure of low oxygen.

Because of this, it is best to perform regular maintenance on your tank. Regular maintenance includes partial water changes every one to two weeks for the tank. 

This will help prevent the oxygen from becoming too low as it will be continuously replenished.

Also, water changes prevent the tank from becoming too dirty. As a tank becomes dirtier, there is accumulated fish waste and algae overgrowth. 

This algae overgrowth will suck the oxygen from the water. Bacteria that form will also break down any excess organic matter. 

Keeping a clean tank can not only help prevent a drop in oxygen levels but also boost it.

Water Movement

A great way to replenish and maintain oxygen levels is to create more agitation in the water to pull in more oxygen into the water. 

This can also be done by placing a high-powered filter system. The higher the filter system the more oxygen will be placed into the water.

An aerator or a bubbler is great for maintaining oxygen levels in the tank. They will constantly be providing additional oxygen to the tank aside from the filter system. 

Another option would be to place an airstone or air pump in the tank.

Another great option is to add a wavemaker to the tank. A wavemaker will increase the oxygen without a pump as it will increase water circulation by breaking the surface tension.

 The waves will move through the surface providing air to contact by causing a gas exchange. Wavemakers are also a great option as you can adjust the speed of the water flow as needed.

Causes of Reduced Oxygen in Tank

High Water Temperatures

As the temperature rises in the tank the oxygen levels will drop. 

Not only does this cause difficulty breathing in the fish but it can also encourage harmful bacteria growth which will further drop the oxygen levels. 

If a temperature rise is the cause of the oxygen drop adjust the temperature to the appropriate temperature. 

For an emergency, you can place ice cubes in the tank to quickly drop the water temperature.

However, for a more permanent solution, it may be best to adjust the temperature of the tank is set to. 

This should only be done if it is within the parameters your fish require. After reducing the overall temperature of the tank the oxygen levels will not drop as easily. 

This is because in cooler waters fish consume less oxygen.


Unfortunately, overcrowding tends to be the biggest reason why oxygen levels drop to dangerous levels. 

As the tank becomes overcrowding with tank mates the amount of available oxygen is lessened by each fish. If overcrowding is the problem in your tank it is best to set up an additional tank to separate some fish. 

Or purchase a larger tank that is more suitable for the amount of fish that you have in your tank.

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