Pond Filter Media Explained: A Complete Beginner’s Guide

Pond Filter Media Explained: A Complete Beginner’s Guide

If you have a backyard water garden or a koi pond, it is likely equipped with a filter to maintain clean and clear water. Perhaps you are thinking about upgrading your filter.

Understanding all the features of a pond filter can be confusing. 

In this blog, you’ll learn the basic types of filtration media and their roles in keeping your pond water clear and healthy. By grasping the basics, you will better understand how your filter works and how to maintain it for optimal performance. 

Understanding the Basics of Pond Filter Media

Navigating through all the infomation on the internet about pond filter media can be overwhelming. This is because varying degrees of accurate information make it challenging to know fact from fiction. 

To simplify, there are three types of pond filtration media: mechanical, chemical, and biological. Understanding these will help you make informed decisions about your pond’s filtration system and evaluate claims more accurately.


mechanical filtration in a pond

Mechanical Filtration: Essential for Pond Clarity

Mechanical filtration means that debris is physically trapped in or on a filter. The size of the debris is larger than the openings in the filter, allowing for its capture, much like how a butterfly net captures a butterfly. 

The most common type of mechanical filter in ponds is a piece of foam. As water flows through, the foam traps larger particles such as leaves, twigs, fish food, and other debris. 

Algae Control: Limitation of Mechanical Filtration

If you notice your pond water turning green, it’s due to millions of single-celled algae actively multiplying in the water. These tiny algae cells are so small they pass through most foam filters. 

When you clean your filter, you might find that the mechanical filter, particularly the foam pad, is clogged with sludge and green algae. While some algae cells may get trapped in the debris accumulated on the foam, this does not mean the filter is an effective “algae remover”. The algae simply got stuck there. Most algae continue to float and reproduce in the water, keeping the color green. 


Pond Skimmers: Enhancing Surface Filtration

You may have read about pond skimmers. A pond skimmer device, similar to those used in swimming pools, is designed to clean the surface of the pond. They work by pulling water from the surface into the filter system. 

Typically placed at the pond’s surface, pond skimmers effectively remove floating debris such as leaves, twigs, and suspended organic matter. By doing this, they prevent these materials from sinking and decomposing at the bottom of the pond, which can otherwise degrade water quality. 

Many pond skimmers have a filter basket to capture larger debris (such as leaves), thereby preventing clogging in the filter intake. Essentially, pond skimmers act as mechanical pre-filters. They are particularly useful in ponds that frequently accumulate leaves or other large debris on the surface of the pond. 


chemical filtration

Chemical Filtration: Advanced Solutions for Pond Purity

Chemical filtration, a term that comes from the aquarium hobby, involves using specialized filter media to remove dissolved substances, toxins, and impurities from water. Unlike mechanical filtration, which targets visible debris, chemical filtration removes dissolved substances from the water. Here are two examples of chemical filtration media. 

Activated Carbon: A Chemical Filtration Powerhouse

Often mistakenly referred to as charcoal, activated carbon is a widely used chemical filtration medium used in both drinking and aquarium water. 

Activated carbon is effective in removing organic compounds, such as yellow tannins that discolor water, pesticides, and various other dissolved substances that can form naturally or enter the pond through runoff. 

Although not commonly used in everyday pond maintenance, activated carbon becomes crucial in situations like accidental spills of lawn chemicals, heavy rain washing surface water into the pond, or unintended pesticide spray drift. In these cases, activated carbon is recommended, alongside a water change. 

Phosphate Removers: Targeting Algae at Its Source

As discussed in our previous blog post on how to manage pond algae, phosphates are known contributors to algae growth in ponds. Phosphate removers resemble granular filter media (such as activated carbon) and are specifically designed to remove phosphates from water

Similarly to activated carbon, phosphate removers are not typically part of standard pond maintenance routines. This is because the most effective and natural strategy for controlling phosphate levels is implementing proper fish-feeding practices (i.e. avoiding overfeeding) and keeping a healthy balance of plants. Overuse of phosphate removers can disrupt the natural balance, leading to an over-controlled environment that might hinder the ecosystems self-regulating ability. 


biological filtration

Biological Filtration: The Natural Ecosystem Balancer

Biological filtration is undoubtedly the most misrepresented form of pond filtration

Biological filtration is a natural process essential for maintaining the health of both natural and man-made ponds, helping to sustain aquatic life.  It involves the recycling and detoxification of fish waste, decaying fish food, and plant material. Biological filtration is driven by millions of microscopic bacteria and other microbes that float in the water and on various surfaces within the pond. 

Biofilter Media: Maximizing Biological Filtration Efficiency

The term biological filter or “biofilter” refers to a specific type of media within the pond filter. 

The idea behind a biofilter comes from sewage treatment plants and large fish-farming operations, that handle a substantial amount of waste material and rely on large, complex biofilters for water detoxification. 

Many pond filters use this concept, by incorporating a biological filter media such as lava rocks, plastic “bio-balls”, and filter sponges, which theoretically provide a large surface area for beneficial microbes to attach to and colonize. While this is necessary for high-waste environments such as a fish farm or a densely stocked koi fish pond, such extensive biological filtration is typically not required for most backyard ponds. Biological filtration naturally occurs on all surfaces of the pond’s environment. The microbes that comprise the “biofilter” will never be isolated to a chamber inside a pond filter. 

Interestingly, biological filter media can sometimes function similarly to mechanical filters. As water flows through biological media, it slows down, allowing suspended debris to settle at the bottom of the filter. 

Pond owners can use the biofilter chamber in this dual role or modify it by adding more mechanical filtration elements such as filter pads or foam to further enhance debris removal. 

Conclusion: Optimizing Your Pond’s Filtration System

Pond filtration can be divided into three simple categories:

  • Mechanical Filtration: This type uses physical filters, such as foam, to trap debris. However, it is important to note that it doesn’t filter out single-celled algae, which are often culprits behind green pond water. 
  • Chemical Filtration: This involves the use of specialized filter media, such as activated carbon or phosphate removers. These materials are designed to absorb dissolved substances, toxins, and impurities from water. 
  • Biological Filtration: This process is centered around the recycling and detoxification of fish waste, decaying food, and plant material, through the action of microscopic bacteria. While some pond filters include biological media such as lava rocks and bio-balls, these are not necessary for most backyard ponds. 

A key reminder for maintaining your pond’s filtration system is the need for regular maintenance. Regardless of the type of filter media you use, it will inevitably accumulate debris and sludge over time. To ensure your filter continues to function effectively and efficiently, it is recommended to replace or clean your media approximately once a month. This routine maintenance is crucial for sustaining peak filtration performance in your pond. 

If you are eager to delve deeper into the world of pond filtration, we recommend reading our detailed guide “Pond Filtration 101: A Comprehensive Beginner’s Guide”. This resource provides additional insights ensuring your pond remains a thriving part of your garden. 

Back to blog

Leave a comment

Please note, comments need to be approved before they are published.

1 of 3