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How to Choose the Best Pond Filters for Your Backyard Pond

How to Choose the Best Pond Filters for Your Backyard Pond

Backyard PondMany homeowners are adding backyard ponds to add a touch of serenity and beauty to their yards. But ponds, like aquariums, can look deceptively simple to maintain. If you don't use the correct pond filters, you could end up with an unsightly and rather stinky mess in your yard.

Were you ever the owner of a goldfish? Did you think all it needed was a nice glass bowl, some food, and a regular change of water?

If so, you were probably a bit disappointed by Goldie's short lifespan.

It turns out, creating the right environment for your goldfish is a bit more complicated than simply keeping the water clean.

The same is true for your backyard pond.

Aside from proper maintenance, the key to establishing a pond system with clear water and healthy plants and fish is using the correct filtration system. The size, location, and types of vegetation and fish in your pond all affect which pond filter will work best.

Why Do You Need a Filtration System?

Ponds that are found in nature obviously function without pond filters. Plants grow in and around them, and fish thrive in them without any manmade interference.

But natural bodies of water will not thrive unless they have the proper combination of a good water supply, a source of oxygen, and the right balance of fish and vegetation so bacteria levels are not harmful. It can take years for this proper balance to be achieved naturally.

With manmade garden ponds, it is possible to speed up this process with pond filters. They keep the water clean and also help maintain the proper biological environment for plants and fish.

What Do Pond Filters Do?

Basically, pond filters perform two important functions: mechanical filtration and biological filtration.

Mechanical Filtration

The purpose of mechanical filtration is to remove debris from the pond, such as leaves, sediment, food, fish waste, etc. This is important, because if too much debris collects in a pond, it can settle to the bottom and decay. This can result in the release of gases that could be harmful to the fish and plants.

Mechanical filtration involves passing the pond water through some type of media, such as sponges or pads. Skimmers pull leaves and other debris off the surface of the pond. Other mechanical filters pull out particles suspended in the water.

While important, mechanical filters are not as important to the health of the pond environment as biological filters.

Biological Filtration

The purpose of biological filtration is to help maintain the proper level of bacteria in your pond. The enemy of a healthy pond environment is ammonia and nitrites.

Decaying plant material and fish waste cause ammonia levels to rise in the pond. Biological pond filters remove the excess ammonia through a process known as the nitrogen cycle. This cycle depends on sufficient levels of bacteria in the system.

Biomedia is contained inside pond filters that allow bacteria to grow that feed upon the ammonia and converts it to nitrites. The nitrites are then broken down by bacteria and converted to nitrates.

This process keeps the pond environment safe for fish and helps keep the water in your pond clearer.

External vs. Submerged Filters

The first decision when evaluating pond filters is whether to use an external or submerged filter.

Advantages of Submerged Filters

The main advantage of a submerged filter is they are generally easier to install and operate. Because they are installed inside the pond, they are hidden from view.

Submerged filters are designed for use in smaller ponds, generally those less than 2,000 gallons. So if you have a large pond, this is not a good option. They can also be more difficult to access for maintenance.

Advantages of External Filters

If you have a larger pond (over 1,000 gallons), you will need to consider using an external filter. These are installed on the outside of your pond.

External filters are easier to install and maintain. They can be more challenging to disguise than in-pond filters, and tend to be noisier.

External filters are also used to create waterfalls in your pond, which can then add attractive elements to your water garden.

So Which is the Right Pond Filter For My Pond?

When choosing a pond filter, size is one of the most important considerations. The rule of thumb is your pump must circulate at least half the water volume of your pond per hour. So with a 1,000-gallon sized pond, you need to circulate at least 500 gallons per hour.

Many experts recommend erring on the side of a larger pump than you think you need, to accommodate other factors such as sunlight, fish, and potential expansion.

For those with small ponds, an internal filter is a popular choice. Make sure you are providing both mechanical and biological filtration with whichever in-pond filter you use.

For external filters, the choices include pressurized filters and gravity return filters.

Pressurized filters

These filters are made up of a cylinder containing the filter and water is forced through by a pump. They are versatile in that they can be installed nearly anywhere around your pond. Water can be passed up to a waterfall or other feature.

These filters are generally best for small to medium-sized ponds.

Gravity Return Filters

Because they do not use pressure, gravity return filters must be located above the water level. Water enters the top of the filter and returns to the pond by gravity.

Also called waterfall filters, these units often contain both mechanical filtration and biological filter materials. They can be used in just about any sized pond.

Other Filter Equipment

Other considerations when choosing the best filter for your pond include whether to also install a UV stabilizer and/or skimmer.

UV Stabilizers

UV stabilizers or sterilizers can support your pond's filtration system. They work by exposing the pond water to high powered UV lights. Often filters will contain a UV stabilizer within the unit. The UV lights kill floating organic materials such as algae and bacteria.

Any pond can benefit from the addition of a UV stabilizer. They are an important tool for keeping your pond water clear.


For ponds located in areas with a lot of wind or nearby trees, skimmers can be very valuable. They can be used in a wide range of pond sizes, from the smallest ponds to those containing thousands of gallons of water.

A skimmer removes large debris that collects on the surface of the water. They only provide mechanical filtration, so must be used in conjunction with a biological filtration system.

A Guide to Pond Installation

Adding a pond to your yard can add to the natural beauty of your landscaping. If you are ready to install a backyard pond to your home, take a look at our guide for building the perfect pond.

For help with your pond supplies, including pond filters, contact us to see our extensive selection of equipment.


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