How to Cure Too Much Oxygen in Fish Tank

Hyperoxygenation: How to Cure Too Much Oxygen in Fish Tank

Oxygen is vital for all living creatures, so too little can be just as bad as too much. A too high concentration of dissolved oxygen is called hyperoxygenation and can be harmful to fish tank inhabitants. Hyperoxygenation can occur naturally or be caused by people adding too much air to the water. The effects of too much oxygen in fish tank are not always apparent, but there are some signs that you should know. 

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What is ‘dissolved oxygen’ in the water of a fish tank?

Dissolved oxygen is the amount of oxygen in the water and can be measured as a percentage. It’s important to have a certain amount of dissolved oxygen for fish to thrive; too much or too little will cause problems for them. When there is too much dissolved oxygen in a fish tank, it can cause a phenomenon called hyperoxygenation, which stresses fish and other organisms.

Image Source: Lapis2380

What happens if there is too much oxygen in a fish tank?

If there is too much dissolved oxygen, it means that the concentration level of carbon dioxide (CO) has dropped too low. This may occur when an overabundance of plants is present, which uses up CO2 quickly through photosynthesis. The process reduces the ability of some types of live rock to absorb CO from aquarium solution, thereby releasing more oxygen into the water column. 

Moreover, hyperoxygenation may also affect the balance in the fish tank affecting fish, coral, and other plants. Too little CO2 also affects this balance and plants need to have that right balance in the fish tank. 

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How much oxygen does a fish need?

Fish needs enough dissolved oxygen to live; the average amount of oxygen required by fishes ranges from 200 and 500 mg of oxygen per hour per kg of fish. However, it may differ in few species. A healthy saltwater tank should maintain an optimum level with no extra supplementation needed. In contrast, freshwater tanks require aquarium air pumps and filters that release some CO2 into the water column, thereby maintaining a lower concentration level than seawater would naturally offer.

How does too much oxygen in a fish tank affect the fish?

High dissolved oxygen levels can lead to hyperoxygenation, which stresses fish and other organisms and is dangerous for invertebrates such as crabs or shrimp. The effects are more pronounced when too little CO2 is present in an aquarium with many plants. Because this increases the availability of O molecules that then bond with H ions; without enough CO2 available to balance out these bonds, they break down quickly into radical pairs. Hyperoxygenated water cause increased mortality rates among fish along with the infectious pancreatic necrosis virus (IPNV) challenge. However, a definite relationship between the both is still uncertain and needs more research. In addition, it could affect gas exchange between respiratory organs too.

How to know if there is hyperoxygenation or too much aeration in fish tank

The signs of too much oxygen in a fish tank are bubbles escaping the surface and increased dissolved oxygen levels. Fish will also show abnormal swimming behavior, open mouth breathing, excessive appetite, or lethargy. If left unchecked for too long, it can be fatal to the fishes’ health.

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You might notice this when you feed your fish and observe that they are eating slower than usual or even not at all, although other factors could also cause it. You can check for too much oxygen levels, too, by looking closely at an air stone bubble closer to eye level on top of the surface. If there’s no sound as it hits the surface, then the chances are high that too much oxygen has been added to your aquarium already.

Signs of too much oxygen in a fish tank includes: 

  • Cloudy eyes: fish cannot see as well due to lack of CO2 Which would generally help penetrate cells for vision.
  • Bloating in your fish: typically occurring when too many gas bubbles get trapped beneath scales causing them to swell.
  • Unexplainable deaths among your fish may also be an indication that you have hyperoxygenation.
Image Source: myaquariumclub

How to avoid hyperoxygenation in your fish tank?

To reduce the hyperoxygenation in your aquarium, you must try the following solutions.

  1. Add more plants to your tank. Plants will consume excess oxygen leaving a higher concentration of CO2 in the water, which is necessary for fish.

  2. Install an air stone or bubbler near the surface of your aquarium that can emit bubbles into the water column. This will pull out the excess oxygen from beneath scales on fishes’ bodies.

  3. Change up your lighting with fluorescent bulbs as they don’t produce as many unnecessary wavelengths as other types such as LEDs. The lights include UV waves which may cause significant damage by breaking down proteins in skin cells and killing bacteria vital to good health. It’s also worth noting that some light fixtures emit too much heat too, so be sure to keep your fish tank away from direct light.

  4. Consider changing the water in your aquarium more often than you might otherwise have done; this can help with oxygenation and reduce harmful ammonia levels as bacteria consume it.

  5. You may want to consider adding a powerhead or filter, so water is circulating instead of just sitting at one spot for too long, resulting in less bloating since fewer gas bubbles are stuck under their scales.

  6. Include live plants if possible, but don’t plant them right next to where the air stone or bubbler emits bubbles; they’ll absorb the excess oxygen.

  7. Monitor your water parameters and make sure you’re performing regular water changes.

  8. Look out for signs of too much oxygen in a fish tank. The signs of excessive oxygen are the same when levels of nitrates or ammonia are too high as well, so keep an eye on those too. 

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The truth is that not all oxygen in the water column should convert into dissolved oxygen for inhabitants. It can be dangerous if too much of the total oxygen content becomes soluble in a system. As this hyperoxygenation leads to decreased levels of carbon dioxide and pH, which are both essential for healthy aquatic life. Though this phenomenon doesn’t happen very often with most tanks because of how easy they are to control. Subscribe to our RSS feed today for more myth-breaking content on everything from saltwater aquariums to keeping your pets happy. 

3 thoughts on “Hyperoxygenation: How to Cure Too Much Oxygen in Fish Tank”



  2. I have two air stones in a 20 gal tank with 2 small fantail goldfish. The smaller one has started hanging out at the top of the tank. I don’t understand why

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