Aquarium Aeration

Jennifer Doll

Jennifer Doll


Aquarium Aeration

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We don’t usually think of fish needing air, but the truth is that aquarium aeration is extremely important for the health and success of your ecosystem. In fact, inadequate aeration is one of the leading causes as to why a fish tank might fail during a power outage.

There are a few ways to increase aquarium aeration, both naturally and with additional equipment. 

Read our guide below to find out why aquarium aeration is important and how to improve the exchange of gases in your own fish tank!

How Do Fish Breathe?

In order to understand why aeration is important, we first need to understand some things about fish physiology and the consumption of oxygen.

As everyone knows, fish have gills instead of lungs, but less commonly known is that the number of gills can differ depending on the type of fish. Some fish have four gills while others, like sharks, can have up to seven. Gills are very similar to lungs, however, and are responsible for oxygen absorption and expelling excess carbon dioxide. 

But fish don’t breathe through their gills. Rather, they inhale oxygenated water through their mouths, which they then move over their gills. The gills are full of capillaries, a series of small and branching blood vessels.

Oxygen dissolved in the water is absorbed by the capillaries, then transported to other parts of the body for various physiological processes. This happens because the concentration of oxygen molecules is lower in blood cells than it is in the atmospheric oxygen of aquarium water.

At the same time, carbon dioxide molecules are released back into the water through the gills. Though it might look like fish are pulling water in through their gills as they open and close their operculum or gill covers, this is a common misconception. They’re actually pushing used water out. 

Think of how we use our mouths and noses to breathe — fish use their mouths and capillaries to turn oxygen to carbon dioxide, and then their gills turn that carbon dioxide into oxygen again, just like our lungs do.

And if you’re ever wondered, “Can fish drown?” Yes, they can. Read more about it here

How Does Oxygen Interact With Water?

Next, we need to understand how fresh oxygen molecules enter and circulate throughout a body of water. 

Oxygen present in water is dissolved oxygen. Water with high dissolved oxygen content can support an abundance of life while deplete areas suffer. There are a few factors that determine the dissolved oxygen concentration in any given location.

Water surface gas exchange 

Oxygen enters the water column through gas exchanges at the surface. Wind and waves help break this barrier between water and air; as we’ll see, this is also why power outages can cause fish to suffocate. 

Simply put, gases are constantly being exchanged between the water and the atmosphere. The dissolved oxygen concentration is then later influenced by changing temperatures and depths, global currents, and photosynthesis. 

Water temperature and depth

Warm water holds less dissolved oxygen than cold water due to its physical properties. As depth increases, the water becomes colder, which means it also holds more oxygen. 

Freshwater systems also hold more oxygen than saltwater ones, mainly due to salinity. 

Photosynthesis and respiration

Photosynthesis is the process performed by plants and other organisms to convert carbon dioxide (CO2) and water (H2O) with energy from light into useable sugar (C6H12O6) and oxygen (O2).

Photosynthesis mainly occurs during periods where light is available, while respiration—the conversion of sugar and oxygen into carbon dioxide and water—usually occurs when light is not available.

In addition to aquatic vegetation, algae, and the photosynthetic zooplankton found in corals, smaller organisms, like phytoplankton, greatly contribute to the overall photosynthesis rates and subsequent dissolved oxygen levels throughout aquatic systems. 

With an adequate oxygen level in the water column, fish, invertebrates, and bacteria are able to breathe and respire. This creates a balanced cycle within the ecosystem, which can easily become uneven if either photosynthesis or respiration rates increase or decrease. 

In extreme cases, increased nutrients can cause algae blooms that create anoxic or oxygen-deficient, conditions which can lead to mass die-offs of the fish population from a lack of oxygen — hence why so many stagnant ponds are riddled with algae and devoid of other life.

Aeration in Fish Tanks

But what about dissolved oxygen in a fish bowl or aquarium?

For the most part, you don’t need to worry about water temperature or depth, though you do need to consider water surface agitation and photosynthesis.

The main way to keep the aquarium oxygenated is to make the tank water flow, especially at the top. Because your aquarium isn’t regularly receiving fresh water input from rain, run-offs, or other bodies of water, the water column can become stagnant.

Surface agitation is necessary to balance the levels of carbon dioxide in the tank. A disturbed surface removes dissolved carbon dioxide while also introducing new gases from the outside atmosphere. Equipment such as air pumps or various types of filters can also circulate the water throughout the aquarium for better-dissolved oxygen distribution. 

If you’ve ever had your power go out, then you know how important it is to manually keep water fresh and moving in your tank. During emergencies like this, temperature and dissolved oxygen are the most important factors in keeping your fish alive.

When the power goes out, fish, invertebrates, plants, and bacteria still respire or start to if they had not been. This quickly depletes the tank’s available oxygen within a few hours or days, depending on the setup. 

To combat this, it’s necessary to stir the water and change it every couple of hours to provide additional aeration and keep your aquarium fish healthy. Many hobbyists choose to purchase a battery-operated air stone for continued surface agitation to prevent situations like this.

The Best Ways to Aerate an Aquarium 

When your aquarium is fully operational, there are a few options for keeping it aerated. 

As previously stated, freshwater holds more oxygen than saltwater —which is part of the reason saltwater aquariums require so much water movement.

Here are some of the best options for aerating your freshwater or saltwater aquarium.

Aerating a Freshwater Aquarium

Aerating a freshwater fish tank is easy and usually doesn’t require additional equipment. In fact, most hobbyists are able to make it work with just proper filtration. 

In freshwater aquariums, wavemakers and powerheads are not the most common equipment to use for aeration. For the most part, they aren’t necessary and can be overpowering for some species of freshwater fish and plants.

This doesn’t mean hobbyists don’t have success with them, though! 


A tank filter is the best way, by far, to aerate a freshwater aquarium. Though they are not entirely necessary if you have a ton of plants, they are efficient at providing adequate surface agitation.

In general, it’s recommended to have a power filter rated for at least double the size of the tank, regardless of using a hang-on-the-back (HOB) filter or canister filter. This provides enough space to house beneficial bacteria and for the output water flow to ensure proper oxygen absorption.

For an even better gas exchange, many hobbyists choose to go with a sponge filter as they directly agitate the surface of the water.

Air stone

This porous stone fulfills a similar role to sponge filters, but they don’t offer any biological filtration. They are inexpensive mechanisms and can be used to introduce and disperse oxygen throughout the aquarium.

The purpose of air stones is simple: introduce oxygen into the tank through fresh air bubbles. The stream of bubbles introduces oxygen directly into the water column and agitates the surface to help circulate water.

It should also be mentioned that some fish love swimming in these beautiful bubbles, and you can pick out a decorative bubble device to add a little more pizzaz to your tank.

Live plants

Live plants are beneficial to aquariums in many ways, but the biggest benefit is aeration. As mentioned before, aquarium plants perform photosynthesis which introduces dissolved oxygen into the aquarium.

However, there is some balance to getting the plant to fish ratio correct. Plants need carbon dioxide in order to make oxygen, and sometimes it’s just not possible to achieve that level with fish alone, especially if you only have a couple of fish.

Many hobbyists inject carbon dioxide directly with a pump, which in turn creates more available dissolved oxygen.

Regardless of how many plants you keep, they will be an indispensable benefit to your system, helping to maintain oxygen and dioxide levels, improving water quality, and contributing to the overall health of the aquarium.

Aerating a Saltwater Aquarium

Aerating a saltwater aquarium is a little different from a freshwater aquarium, but not by much. 

One of the major differences is in the use of air stones. Air stones aren’t commonly used in saltwater setups as they can potentially irritate corals and cause a lot of foam/salt creep. Some believe they can also affect pH, though this has yet to be confirmed.

Instead, try using other conventional methods first.

Filtration and plumbing

Filtration and plumbing are necessary for aerating a saltwater aquarium.

Saltwater aquariums can successfully be kept with a box filter, canister filter, or sump, but sumps generally provide the best opportunity for aeration due to the abundance of movement between the tank and the sump, as well as in the sump itself.

In addition, many sumps include refugiums that can house photosynthetic algae species as well as protein skimmers that create air bubbles. 

Both canister filters and sumps usually allow for control over return nozzle direction, which can alter the turbidity of the surface water. Otherwise, an overpowered HOB filter can create similar results depending on the filter outflow and filter placement.

Wavemakers and powerheads

Another necessary piece of equipment for saltwater aquariums is a wavemaker or powerhead. These machines simply circulate water but can be used to agitate the surface if positioned as so. 

Furthermore, multiple wavemakers and powerheads can be positioned at different levels of the tank so that oxygen is delivered throughout the system effectively.

Corals and algae

Similar to aquatic plants, corals and algae can introduce more oxygen into the water. However, these usually take a little more work and setup than introducing simple freshwater plant life.

Corals themselves are not photosynthetic. Instead, they have a symbiosis with a type of dinoflagellate called zooxanthellae that undergo photosynthesis and produce oxygen. 

As mentioned before, refugiums can house algae — specifically macroalgae. Not only are these species efficient at absorbing nutrients, but they also produce oxygen. That said, they are extremely fast-growing and need to be controlled for nutrient uptake, or else they can create anoxic conditions in extreme circumstances. 

Macroalgae can also be kept in the main display, whether they are wanted or unwanted species. 


Aquarium aeration is one of the most important factors of keeping a successful freshwater or saltwater aquarium. Fish and invertebrates need oxygen to breathe through their gills to complete bodily functions. 

Aeration can be achieved through several organic methods and mechanisms, but is most efficient when dealing with the surface layer of the aquarium and further creating water circulation throughout the rest of the aquarium. 

If you have any questions about aeration in freshwater or saltwater aquariums, the different kinds of aeration equipment you can use in your own aquarium to increase circulation, or if you have had experience eradicating dead zones from your own setup, don’t hesitate to leave a comment below! 

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