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Pond Aerators: How They Work and Why You Need One

Pond Aerators: How They Work and Why You Need One

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Paul Brown

It is easy to understand why ponds and other water features are so popular among homeowners. They add beauty to the landscape and create a relaxing oasis right in your own backyard…as long as they are properly maintained.

One key element of proper pond maintenance is aeration. There are a variety of different aerator types that all serve the same purposes:  increasing the amount of oxygen in the water and circulating oxygenated water throughout the whole pond. Without an aerator, your pond will become a stagnant haven for muck, mosquitoes, and other undesirable species.

Purpose of Aerators

Aerators serve two primary purposes:

  • Promoting oxygenation
  • Improving water circulation

Without these two processes, the pond and its ecosystem will suffer.

It is important to note that not all aerators are circulators and vice versa. The size and depth of your pond, as well as your personal preferences, will determine if you need both devices or just one.


All animals and plants need oxygen to survive. In natural bodies of water, the oxygen from the atmosphere combined with the oxygen released from underwater plants is enough for the fish and other species in the ecosystem. The supply of oxygen and the demand for it are fairly evenly balanced.

In landscape ponds, however, the demand for oxygen is often much higher than the supply. This is because landscape ponds are more densely populated with fish, plants, and microbes. They take up less surface area than natural ponds or lakes, but they contain a higher number of species per cubic foot. 

Aerators solve the problem of this high demand by oxygenating the pond water. They create turbulence, which allows the water to collect more oxygen from the air than it collects by sitting still. Even small drops and bubbles increase the amount of oxygen available to the pond’s wildlife (source).


Oxygenation is just the first step. The next step is circulating the freshly oxygenated water so that it feeds wildlife across the width and at every depth of the pond.

This process does not happen automatically because of stratification. Stratification happens when the water’s surface becomes warm from the sun, but the deeper layers of water stay cool. The layer of warm water does not mix with the layer of cool water.

Stratification is a problem because those warm surface layers contain the highest concentration of oxygen. Since the warm and cool layers don’t mix together naturally, oxygen levels near the bottom of the pond are likely to be depleted.

When water is mechanically circulated, it can’t separate into distinct warm and cool layers. Aerators prevent stratification by forcing the water up from the bottom and circulating oxygenated water back to the pond’s depths (source).

Consequences of Not Aerating and Circulating

Failing to aerate and circulate your pond can have several negative consequences, including:

  • Fish kills
  • Stagnation
  • Eutrophication

Fish Kills

Whether you plan to keep just a few koi or a full stock of different fish species, aeration is critical to their health. This is especially true in the winter.

When the surface of a pond freezes over, it can’t take in any more oxygen from the atmosphere. If sunlight can still get through, aquatic plants can continue producing oxygen through photosynthesis, which may be enough.

However, when the pond’s surface is covered by both ice and snow, photosynthesis will not take place. If the pond contains a good deal of aquatic plants, fish, and algae, they will compete with each other for the remaining oxygen until it completely runs out.

If you live in an area that experiences abundant ice and snow, mechanically aerating your pond can keep your fish and plants alive throughout hard winters. You won’t need to aerate as often, since fish’s oxygen needs are lower during cold weather, but occasional aeration can keep them healthy (source).


Stagnation happens when water stops flowing. Stagnation can occur during any season, and it is never desirable. 

Still water doesn’t stay fresh for long. It becomes stagnant by collecting animal waste and providing a home for bacteria. When left alone, stagnant water develops “muck” very quickly, which is both unsightly and smelly.

Worst of all, though, stagnant water is the one and only breeding location for mosquitoes, including the species that spread diseases.

Female mosquitoes lay their eggs in stagnant water. After the eggs hatch, mosquitoes live in the water throughout their larval and pupal stages, feeding on microbes that thrive in stagnation. When the temperatures are warm enough, a mosquito can complete its entire growth cycle–egg to adult–in less than one week.

The bad news is that no homeowner, even those without ponds, can make their yards one hundred percent mosquito-proof. 

The good news is that aeration and circulation make your pond less attractive to breeding mosquitoes because they avoid moving water and turbulence. Moving water is simply not conducive to their survival.

Furthermore, aerobic bacteria–microorganisms that breathe oxygen–break down animal waste and other muck 20 times faster than anaerobic bacteria. Keeping your pond aerated allows these bacteria to thrive, which keeps muck to a minimum (source).


Eutrophication is the pond’s natural aging process. This may not seem like a problem, and it may also seem unavoidable. To some degree, that is true.

Put another way, however, eutrophication is the process through which a pond becomes a bog. Even artificial landscape ponds can turn into backyard bogs if eutrophication is allowed to run its course.

A new pond begins with only a few nutrients and a small amount of aquatic life. Before long, the pond contains more nutrients, which encourages new aquatic life. When these plants and animals die, they return the nutrients they consumed back to the pond.

Eventually, the pond becomes increasingly shallow, thanks to the continued accumulation of decay, waste, and nutrients. Finally, the pond completes the eutrophication process by becoming a bog. Depending on the size and depth of the pond, complete eutrophication can happen in as little as a decade. 

No homeowner wants to see their lovely pond turn into a shallow, smelly bog. Eutrophication will occur even if you don’t keep fish or plants in your pond. Aeration and circulation play important roles in slowing down the eutrophication process.

First of all, once again, aeration is necessary to the survival of the aerobic bacteria that break down waste and decay, allowing it to be flushed out of the pond.

Second, aeration keeps aquatic animals and plants healthy by meeting their demand for oxygen. This prolongs their lifespan, limiting the accumulation of decay.

Third, circulation prevents excessive build-up of nutrients. Many backyard ponds include a filtration system; circulators move the water through the filters, flushing out excess nutrients in the process (source).

Installing an aerator is a small price to pay to avoid fish kills, stagnation, and eutrophication!

Pre-Purchasing Considerations

Whether you’re planning to install a pond, or already have one but need to choose an aerator, there are several considerations you need to make first. The answers to these questions will help guide you to the right aerator:

  • Do you plan to keep fish in your pond? If so, you will need an aerator that thoroughly circulates your pond water, even in winter, if necessary.
  • Do you intend to grow any plants in your pond or around its perimeter? The more plants you grow in your pond, the higher the demand for oxygen will be. This demand will be even greater if you keep fish in your pond, as well.
  • How large and deep do you want your pond to be? Some aerators will not be effective in high volumes of water.
  • How much space do you have? Some very effective aerators are quite large. Keep their size and the available space in mind as you plan your pond landscape.
  • Do you have any children or pets? All ponds and water features are a liability to some extent. Certain large and powerful aerators may increase the safety risks of owning a pond.

Types of Aerators and Their Functions

As mentioned above, not all aerators are circulators and vice versa. Many devices are designed to oxygenate and circulate water, but it is necessary to know their functions before you buy. No two devices function in the same way, and each one brings advantages and disadvantages to the table.

The following are the most common types of pond aerators:

  • Bubblers/diffusers
  • Circulators
  • Fountains
  • Pumps
  • Paddlewheels


The terms “bubbler” and “diffuser” are often used interchangeably when referring to pond aerators. These devices work to oxygenate and circulate water, so they will be an excellent option for many pond owners.

Diffusers have two main components:  an air blower or compressor that is mounted outside of the pond and a diffuser pad attached to the bottom of the pond. The blower and diffuser pad are connected to one or more air hoses.

The air blower forces air through the hoses where it is released through a series of small holes in the diffuser pad. The air creates bubbles which release oxygen into the water.

The force of the air is also strong enough to generate a vertical current. Vertical currents combat stratification by moving water from the bottom of the pond up to the top, keeping the water circulating as long as the diffuser is running (source).

Bubbler/Diffuser Advantages

  1. They are extremely effective in ponds that are 10 feet deep or deeper.
  2. A single blower or compressor can supply air to multiple diffuser pads. If you have a large pond, you can spread out the diffuser pads strategically so that no part of the pond is neglected.
  3. Solar and wind-powered diffuser models are available to purchase. This is extremely convenient for pond owners without a nearby source of electricity. Solar and wind power are also free once the equipment is installed!

Bubbler/Diffuser Disadvantages

  1. They are not very effective in shallow ponds that are less than eight feet deep. This is because the bubbles rise to the surface too rapidly to transfer enough oxygen to the water. You can buy low airflow diffuser systems to offset this problem, but they tend to clog easily (source).
  2. Bubblers must run continuously to be at their peak efficiency levels, but solar and wind-powered models are not equipped for continuous use. Unless they have attached batteries, they will stop running at night or when wind speeds are low (source).


As their name implies, circulators are designed to circulate water throughout the pond. Some models only provide circulation; others include attachments that aerate the water, too, by forcing bubbles into the water.

There are two main circulator types:  floating and submersible. The floating models are more common for backyard ponds because submersible models require mounting on a pier, dock, or other structure.

Both circulator models run on motors that power propellers underneath the surface of the water. The propellers generate enough force to move large quantities of water.

Circulator Advantages

  1. Circulators’ propellers are adjustable. Pond owners can change the angle of their position to accommodate the depth and width of the pond.
  2. Circulators’ specialty is preventing stratification. Because they can easily circulate high volumes of water, they often eliminate stratification altogether.
  3. Circulators are perfect for small ponds and ponds that don’t have much wildlife. When the demand for oxygen is fairly low, circulation is more important than increasing oxygenation.

Circulator Disadvantages

  1. The only downside with circulators is that their aerator functions may not provide enough oxygen to meet your needs. If you want to keep quite a few fish or plants, you may need a device that does more oxygenating (source).


Fountains are popular options because they add visual interest to a pond. They come in a variety of models that can be programmed to propel water to different heights, to a certain rhythm, or in varying spray patterns.

The fountains designed for home usage are often floating models anchored near the center of the pond. If your pond is large enough, you may have room for more than one.

Fountains aerate the pond’s water by creating turbulence and agitation.

Fountain Advantages

  1. Fountains are the most aesthetically attractive type of aerator.
  2. There are a wide variety of fountains available to buy.

Fountain Disadvantages

  1. Fountains do provide some aeration but not nearly as much as other aerators. Their strength is their visual appeal rather than their usefulness.
  2. Fountains are not circulators. The water they do oxygenate tends to stay within a small radius of the fountain itself (source).


There are multiple kinds of aerator pumps available for pond owners, but two of the most common kinds are pump-sprayer aerators and vertical pumps.

Pump-sprayers are very large and require high-powered motors to run. These would be good choices for people whose ponds are large enough to stock catfish or use for swimming or canoeing. 

Vertical pumps, on the other hand, are designed for shallow ponds. Like fountains, they float on the pond’s surface; unlike fountains, they don’t propel the water very high.

Depending on the surface area of your pond, you may need more than one vertical pump.

Pump Advantages

  1. Unlike some other aerator types, pumps function well in shallow water.
  2. Vertical pumps have high aeration efficiency.

Pump Disadvantages

  1. Vertical pumps are aerators only; they don’t provide good circulation. Depending on the depth and surface area of your pond, a vertical pump may not be enough on its own (source).


Paddlewheels are cylindrical drums with staggered arrangements of metal or plastic paddles. The drum is attached horizontally to a floating platform on the pond’s surface. A motor rotates the drum, and the paddles lift and splash the water.

Like pumps, paddlewheels come in models large enough for catfish ponds and small enough for landscape ponds. 

One reason paddlewheels are popular for large ponds is because they are extremely energy efficient. For every dollar spent on electricity, they provide more oxygen than any other aerator. They are also powerful enough to circulate the water a considerable distance.

Paddlewheel Advantages

  1. Paddlewheels are very effective aerators and circulators.
  2. They are high-powered yet energy efficient.

Paddlewheel Disadvantages

  1. Paddlewheels are among the most expensive aerators on the market.
  2. Paddlewheels are effective at circulating surface water, but they don’t circulate water very deeply. If stratification is a concern for you, a paddlewheel may not be the best choice.
  3. They are heavy and not as visually attractive as other aerators and circulators (source).

Buying an Aerator

Pond aerators and circulators are available for purchase at home improvement stores, tractor supply stores, garden centers, and online retailers. There are also specialty suppliers who deal only in pond supplies and maintenance.

Costs will vary widely by aerator type, manufacturer, and model. Remember to factor in electrical costs and ongoing maintenance.

Click here to view a popular pond aerator and browse other options (link to Amazon).


Avoiding problems like stratification, stagnation, and eutrophication in your backyard pond seems like a complicated task. However, combating these problems is much simpler with the right aerator.

The right device will depend mostly on the size and depth of your pond, but aerators are not an optional add-on or pond accessory. They are crucial to maintaining a healthy pond environment, especially for fish and plants.