What to Consider When Buying a Pond Filter

Pond filtration is necessary for maintaining a clean and balanced ecosystem in your pond. There are different kinds of filters and filtration, and each has its advantages for certain types of ponds. This process can be overwhelming, so to help you out we’ve put together some essential information about pond filtration systems and guidelines on choosing the right one for your pond.

To better appreciate why filtration is a good idea, you need to understand how it works. Filtration is needed to eliminate muck, particles, and biological wastes from the water that are unhealthy for the pond. A properly installed filtration system will pull water from the bottom of your pond and circulate it, along with essential nutrients and oxygen, throughout the water garden. There are natural ways of filtering, but help from man-made filters and pumps help speed up the process of filtration. Even if your pond is solely decorative, a filtration system will help prevent stagnation, reduce algae growth, impede insect pests, and clean the water to be used in a beautiful water display.

Now that we understand why filtration is important, let’s talk about the different types of filtration methods. The right choice for your pond will be based on the size of your pond, water depth and volume, and the number of plants and fish that are present in it.

Types of Filtration

Mechanical or physical filtration refers to the removal of particles of debris by means of passing the pond water through various filtration media. Skimmers, canister filters, and pre-filters are common examples of filters that mainly rely on mechanical filtration. Depending on the type of filter, this filtration method keeps the water clear by straining, skimming, or trapping leaves, muck, algae, and any other form of debris. This helps to prevent clogs in other pond equipment as well as reduce the build-up of debris from settling on the bottom. When run through a mechanical filter, water will not be treated and will retain any toxins or harmful substances it contained prior to entering the filter. This type of filter is not recommended as the only source of filtration for a pond containing fish or aquatic wildlife. Mechanical filtration systems need to be regularly cleaned, at least once a week, to ensure that the filter is functioning well and is free from excess solid waste.

Chemical filtration is more commonly used in aquariums, but some pond filter systems do use it. As the name implies, it uses chemicals to remove organic and inorganic pollutants with specialized media like carbon and resins, usually in a loose, bagged, or pad form. This method is usually used to manage ammonia levels or to remove any traces of medication or treatment used in the pond.

Biological filtration removes toxins from your pond water and provides a safe and healthy environment for your aquatic wildlife. Biological filtration works by incorporating a filter in or around your pond that uses bacteria in order to break down toxins coming from fish, excess food, and decaying organic material. These types of filters break down the ammonia in the water into nitrite. Later on beneficial bacteria will develop, transforming the nitrite to nitrate, which are not as harmful to fish and are used by plants. Biological filters typically clean the water through mechanical filtration as well as treating the water and removing toxins. Many pond owners use only biological filters due to the dual filtration associated with this method.

Ultraviolet Clarifiers are not really considered filters, but UV clarifiers are often used in combination with a filter or actually inside the filter itself. UV clarifiers are designed explicitly to tackle the problem of green murky water due to algae blooms. UV clarifiers kill floating algae, bacteria, and other microorganisms that flow through the clarifier and return clear, safe water back to your pond.

Filtration systems include a filter and a pump. As mentioned above, filters are used to remove any unwanted solid particle that can damage your pond. Pumps, on the other hand, are vital for passing water through the filter. As a pond owner, you must first decide whether your pond will require complete biological filtration due to aquatic life or, in the case of a small decorative pond, simply require a mechanical filter.


There are many different types of filters. There are combination, external, and submerged filters. Combination filters are multi-functional and perform the duties of different types of filtration. For instance, a multi-filter may include sponge media that absorbs debris and an empty chamber to add "tea bags" of chemical media that help break down unwanted pollutants and particles. Meanwhile external and submerged filters are either located underneath the pond’s water or out of it. When deciding between these two filter types, consider important factors such as pond size, plumbing, required electricity, and installation. Submersible filters are installed directly in the pond, intended for smaller ponds, easier to plumb and disguise, but harder to maintain and wire for electricity. External filters are installed outside of the pond, intended for larger ponds, easier to maintain and wire for electricity, but harder to plumb and disguise.


Water pumps are perhaps the most important piece of equipment for a good filtration system. Similar to choosing water filters, selecting a pump for your pond will depend on many factors. An important thing to look for in a pump is its ability to cycle water in your pond. You should also become familiar with pump pressure and pump volume. Pressure is how quickly the water is circulated, and volume is how much water is circulated. A good choice for ponds is a low-pressure, high-volume pump. Experts say that a pump should circulate all of the pond water through the filter in a period of 60 to 90 minutes. Experts also suggest in investing in a good quality pump. It may be more expensive at first, but it can be more cost-effective in the long run. Cheaper pumps may use more electricity, may break down more often, and will cost more in the long run than a high quality, energy efficient pump.

When choosing a filter and pump for your pond, make sure that the filter size is sufficient and water circulation is adequate in all areas. As you head out and search for the right type of filtration for your pond, here are some factors to consider. Determine the volume of water in your pond by measuring the length, width, and depth of your pond and use this formula: Length x Width x Depth. Decide what you want your pond to be like. Do you want more plants or fish or both? The presence or absence of plants and fish will impact the amount of debris build-up and existence of bacteria in the pond, which are major factors to consider when choosing a suitable filtration system. The amount of sunlight your pond is exposed to can determine which filtration system is used. A lot of exposure to the sun can lead to excessive algae growth, which will require more intensive filtration.

Keep in mind that a high-quality filtration system provides many functions including enhancing water quality, managing ammonia and nitrite levels, ensuring water movement and adding oxygen to the water. The filtration system is almost certainly the most important piece of mechanical equipment in your pond, so spending more on a system that is easy to maintain and of the best quality is to your advantage.