Can a Fish Have Too Much Oxygen In The Tank?


Oxygen is one of the most essential gases needed in your tank for your fish’s survival. Your fish uses this oxygen for respiratory functions. The amount of oxygen in your tank (dissolved oxygen) is measured in percentage. This oxygen is essential for the process of metabolism and breathing, so when deprived of oxygen, your fish can die just as it is in humans.

As we all know too much of everything is bad, does it also apply to too much oxygen in a tank? For your fish to thrive, there is every need for the oxygen level to be sufficient for your fish. Anything less than that can cause distress to your fish and if the tank is not properly aerated your fish is likely going to die.

You can add an aquarium air pump to your tank for proper aeration in the tank. When the oxygen level is low, it is bad for your fish. How about when there is excess/ too much oxygen? Does it have any negative impact on your fish? Read along so you can know if you can allow too much oxygen in your fish tank.

Can a Fish Have Too Much Oxygen In The tank?

Too much oxygen is bad for your fish just as too little oxygen is. Most time too much oxygen happens when there is an abundance of plants in your tank. These plants use up carbon dioxide fast during the process of photosynthesis and give off oxygen. The Concentration of Carbon dioxide drops and that of oxygen elevates.

Too much oxygen can also be a result of using an aquarium air pump to aerate the tank. When using an air pump, you need to regulate the amount of air and not allow the tank to work all day long.

A high level of dissolved oxygen stresses your fish. If your tank has crabs or shrimps, then it can be dangerous to them. Too much Oxygen means too little carbon dioxide and this can increase the level of mortality in your tank. It can also affect the exchange of gas in your fish’s respiratory organs.

Too much oxygen in your tank can be detected using an oxygen test kit. Another way of detecting high oxygen levels is by monitoring the tank. You will notice a lot of bubbles escaping from the surface of the tank, your fish might suddenly develop an abnormal swimming pattern, lethargy, and excess appetite and you might notice your fish having an open mouth breathing.  Hight level of dissolved oxygen needs to be checked and solved if not it can be fatal to your fish’s health.

How Much Oxygen Does Your Fish Need In a Tank?

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The average amount of oxygen needed for your fish is about 200-450mg per hour per kg of fish. This can differ depending on the species of fish you have in your tank. Fishes have a different level of oxygen needed so too much oxygen for this specie can be normal for another specie. You have to consider the specie of your pet fish.

A saltwater aquarium can maintain an optimum level of oxygen without the need for external aid. Contrary to saltwater, a freshwater aquarium requires a filter and sometimes an air pump for proper aeration and balancing the oxygen-carbon dioxide level in the tank.

What Are The Signs Of Too Much Oxygen In a Tank?

Some signs will indicate too much oxygen in your tank. You might notice one or more of these signs when having your quiet evening time enjoying the sight of your aquarium. Detecting it early will help you solve and bring the oxygen level back to normal before it causes major damage to your fish. Some of these signs are;

  • Open mouth breathing: You will notice your fish opening their mouth and gasping for breath, this is one major sign that there is too much oxygen in your tank
  • Cloudy eyes: Too much Oxygen means too little carbon dioxide, and when the carbon dioxide level is low, your fish cannot see clearly. Carbon dioxide helps in the penetration of the cells for vision in fish.
  • Bloating: This is a result of too many bubbles getting trapped in the fish’s scale and making them swell.
  • Excess appetite: Oxygen is responsible for metabolism. Too much oxygen will increase the metabolism rate and this will increase your fish’s appetite.

How Do You Avoid Too Much Oxygen In Your Tank?

There are various ways/ measures to take to avoid too much oxygen in your aquarium. Some of them are;

  • Add an air stone to your aquarium. The air stone should be kept near the surface so it can emit bubbles into the water column. This will help pull out the excess oxygen that forms bubbles in the fish’s body or under its scale. You can use a bubbler in place of an air stone.
  • Regularly check your water parameters, this will help you detect any chemical imbalance on time.
  • Add in more plants. They will consume the excess oxygen and cause more carbon dioxide in the water. This way the oxygen and carbon dioxide levels will be balanced.
  • Regularly change your aquarium water. The water doesn’t have to be dirty before you consider a change. By changing it on regular basis, there will be a normal supply of oxygen. It will also help reduce the level of ammonia in the water.
  • Adding a filter will also help in regulating the oxygen level. It will make the water continue to circulate and not be stagnant, and by so doing there will be less bloating and few to no gas bubbles getting sticker under your fish’s scale.
  • Some types of light produce unnecessary wavelengths. Using fluorescent light is going to be a great option because it doesn’t produce unnecessary wavelengths. 
  • Including live plant is one good way of regulating the oxygen level because they will help absorb the excess oxygen. Do not plant them close to the air stone or bubblers
  • Always monitor your tank and watch out for the signs of excess oxygen. Some of the signs are similar to that when nitrates or ammonia are high in the tank. You need to also watch out and monitor them as well.

When you notice any of the above signs, you can use a test kit to confirm the level of oxygen. When it’s confirmed that the dissolved oxygen level is high then you can take the necessary measure required to bring the level back to normal.


Oxygen is essential for your fish, but just like any other thing, it can be bad when taken more than necessary. Too much oxygen is bad for your fish and if not solved on time can be fatal. You can detect too much oxygen by observing your fish or by checking the oxygen level using a test kit.

Some of the possible behaviour you will notice when there is too much oxygen is, excess appetite, lethargy, open mouth breathing, and too many bubbles at the surface of the tank.

When you notice any of these, you can test for the oxygen level to confirm and if it is what you suspect, then you take the necessary measure to bring the oxygen level to normal for the healthy benefit of your finned friend.

Written by Justin Michaels

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