Do Aquatic Plants Produce Oxygen For Fish In Aquariums?

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Aquatic plants benefit aquariums by absorbing carbon dioxide (CO2) and ammonia (NH3) that your fish generate, and in return, aquatic plants produce oxygen (O2) that your aquatic fish can utilize for respiration.

While pH, temperature, and salinity are all important for fish tanks, dissolved oxygen (DO) is one of the most important properties of water quality that aquarists must understand. 

Oxygenation is essential for a healthy aquarium environment, and while fish require oxygen to survive, other reef inhabitants also rely on this vital resource.

Many aquarium hobbyists are surprised to learn that aquatic organisms like fish cannot utilize oxygen from H2O (water) molecules. Water molecules contain a single oxygen (O2) molecule bound to two hydrogen (H2) molecules, making it an unusable form. Therefore, ‘usable’ oxygen is dissolved into aquarium water via diffusion from the surrounding atmosphere and as a byproduct of aquatic plant photosynthesis. 

Do Aquatic Plants Produce Oxygen In Aquariums?

The biggest benefit to adding aquatic plants to your aquarium is that they produce oxygen and remove carbon dioxide (CO2) and ammonia (NH3) produced by your fish. However, plants can only do this during daylight hours when they undergo photosynthesis from your aquarium lighting.

During the day, aquatic plants absorb CO2, producing O2, and during the night they absorb O2 and produce CO2. However, you will rarely experience oxygen shortages during the night or dark phase of your lighting cycle, unless you are solely relying on aquatic plants as an oxygen source for your fish. 

Most of the O2 in your aquarium will come from dissolved oxygen at the water surface, where the surrounding air can be diffused/dissolved into the water. Therefore, the amount of oxygen your aquatic plants produce is minute compared to the amount of O2 dissolved from the outside environment. 

Aquarium Plants That Produce The Most Oxygen

As aforementioned, aquarium water does not contain as much oxygen as the surrounding air we breathe, therefore, aquariums rely on other sources for oxygen, one of them being aquatic plants. 

Some aquatic plants are much better at producing oxygen than others, these include:

  • Hornwort
  • Eelgrass (Vallisneria)
  • Green Cabomba
  • Red Ludwigia
  • Anacharis

How Much Oxygen Do Fish Need In Aquariums?

Oxygen requirements vary between fish species, however, it is recommended your aquarium water has an 80-110% oxygen saturation and DO level of 6-8 mg/L. 

Supersaturation (anything >115%) in aquariums should be avoided, as it can cause gas bubble disease in your fish. 

Symptoms Of Low Oxygen Levels In Aquariums

  • Labored breathing 
  • Rapid gill movements
  • Gasping at the surface*

*Gasping at the surface must not be confused with the natural behavior of labyrinth fish. Fish such as Bettas, Gouramis, and bottom-feeder Catfish will regularly swim to the surface and gulp air using their labyrinth organ. This doesn’t take too long, so if they are spending most of their time at the surface, it is likely your fish tank has low O2 levels.

Other Ways To Increase Oxygen In Aquariums

As many aquatic plants cannot sustain heavily-stocked fish tanks, there are other ways to increase the amount of oxygen inside your aquarium you should consider. 

Temporary Methods

If your aquarium suffers from an oxygen drop overnight, you should immediately:

  • Pour water from a height
  • Perform a large water change 
  • Manually stir the water

Permanent Methods

When keeping an aquarium, particularly if you have a lot of fish that produce waste, you should use one or more of the following to increase oxygenation in the water long-term. 

  • Water pumps – hang on back (HOB) filters are highly recommended
  • Spray bars
  • Air pumps
  • Air stones 
  • Air bubblers

What Affects The Amount Of Dissolved Oxygen In Aquariums?

The amount of dissolved oxygen in an aquarium can affect your aquarium oxygen supply and the water quality. Several factors can influence dissolved oxygen levels in the water, these include:

  • The amount of aquatic life (fish, plants, and algae) present. 
  • Salinity – as salinity increases, dissolved oxygen is decreased. 
  • Water temperature – as temperature increases, the less oxygen the water can hold. 
  • Atmospheric pressure surrounding the aquarium. 
  • The amount of water flow/movement inside the aquarium.

If your dissolved oxygen levels are too high, you can easily remove DO from the water using physical and chemical techniques such as thermal degassing, vacuum degassing, countercurrent exchange, nitrogen striping, and using nutrients and more plants inside the aquarium.

How To Measure The Amount Of Oxygen In An Aquarium

The most accurate way to measure O2 in aquariums is to use an oxygen sensor or dissolved oxygen kit

Instructions on how to use a DO probe/sensor can be found here

What Other Benefits Do Aquatic Plants Have For Fish?

Aquatic plants are not limited to only producing oxygen for fish, they are also very useful in:

  • Removing CO2 in heavily-stocked fish tanks. 
  • Absorbing ammonia, nitrates, and nitrogen, which are harmful to fish. Despite absorbing these harmful products, you will still need to perform regular water changes.
  • Creating a protective sanctuary for fish and fry. 
  • Promoting substrate security via the plant roots. 

Conclusion

Earth consists of around 71% water, and all forms of life rely on oxygen that is dissolved in the water to survive, including the fish inside your aquarium. 

Oxygen levels can be increased by adding aquatic plants such as Hornwort, Eelgrass, Green Cabomba, Red Ludwigia, and Anacharis, however other methods such as air stones and water pumps are recommended to maintain oxygen levels in heavily-stocked fish tanks. 
If you have any questions regarding dissolved oxygen, or you would like to learn more about other water quality measurements, characteristics, or applications for DO, please do not hesitate to contact our world-class team at Atlas Scientific.

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