The Most Effective Way to Filter Pond Water

One of the most popular misconceptions consumers have today about pond ownership is that it’s too high maintenance. They’ve heard myths and horror stories about algae taking over, fish dying, mosquito infestation, smelly water, and more. Many consumers believe in order to have a pond with clean and clear water, they’ll need to spend hours maintaining their pond. This simply isn’t true if proper steps are taken to create an ecosystem pond that works with Mother Nature, not against her.

In addition to plants, fish, aeration, and rocks and gravel, a low-maintenance ecosystem pond requires adequate filtration to help keep the water healthy and clear.  A good biological filter paired with a proper mechanical filter is the most effective way to ensure a naturally balanced ecosystem pond.

The Job of a Pond Skimmer

The main function of a mechanical filter, or pond skimmer, is to remove debris before it sinks to the bottom of the pond and decays. The skimmer also houses and hides the pump and plumbing from view.

Aquascape skimmers come with either a horizontal filter mat or an optional brush cartridge.  Horizontal mats prove to be the most effective, while providing the least amount of maintenance. Horizontal filter mats lay flat and won’t sag and lose their shape like vertical mats often do.  They also never clog to the point of preventing water from passing through, so the pump chamber does not run dry.

As water enters the skimmer, large debris is captured in the debris net or basket. The water is then further filtered through the horizontal mat.  The pond water travels through the plumbing buried underground, up to the biological filter where it’s further treated before re-entering the pond.

Biological Filtration Goes to Work

The biological filter receives water that has already passed through the skimmer and is typically placed on the opposite side of the pond.  The water enters the biological filter via flexible pipe located near the base of the unit.  The water then flows from the bottom to the top of the filter, traveling through filter media housed inside the unit.  The filter media helps with the removal of fine to medium-sized particles.  The larger debris was already removed by the skimmer. 

As the biological filter fills, it overflows and cascades over its waterfall lip, cascading down rocks that have been set to create a beautiful and natural-looking waterfall.  The waterfall creates aeration for the pond, assisting in the circulation and health of the water.  If a slower, stream effect is preferred, the biological filter simply needs to be sunk lower into the ground.

Biological filters on the market today range in size and can filter ponds up to 10,000 gallons.  For larger ponds, multiple biological filters can be incorporated into the design.

The Science Behind the Design

Mechanical and biological filters are critical to processing the many types of nutrients found in a water garden system, including fish waste, uneaten fish food, leaves, and runoff from lawns to name a few.  High levels of ammonia (a form of nitrogen) are highly toxic to fish and are a major contributor to prolific algae growth, and so they need to be carefully controlled.  In water gardening, the primary nutrient that biological filtration utilizes and renders usable is nitrogen.

In biological filtration, nitrifying bacteria, known as facultative bacteria, absorb ammonia and turn nitrites into nitrates, which are less dangerous. These bacteria require oxygen to live, so it’s important for the pond pump to run 24 hours a day, 7 days a week.  If the pump isn’t running, the waterfalls aren’t flowing, and aeration is eliminated from the necessary equation to maintain an ecosystem pond.  Keep in mind that if the pump shuts down, the bacteria will quickly use up all the oxygen and die.  This isn’t a good thing.

Nitrates are removed from the pond by another biological filtration method known as de-nitrification.  This process occurs only in anaerobic (without oxygen) areas of the pond.  That’s why it’s not necessarily bad for some areas of the pond to experience minimal water flow (such as on the bottom of the pond, under an inch or so of gravel).  The bacteria that live in this area of the pond turn nitrates into nitrogen gas, which is released into the atmosphere. Nitrates are also absorbed by aquatic plants and algae during their growth processes. A pond without aquatic plants will prove to be a maintenance nightmare.

For any biological filtration to work, there literally needs to be billions of bacteria working to purify the water.  They prefer to anchor onto things, which is why surface area is so important. More surface area means more bacteria, and more bacteria means better biological filtration.  Surface area is provided by filter media, rocks, and gravel.  A pond with gravel on the bottom will contain more surface area for bacteria, as opposed to a pond with exposed liner on the bottom.

The Role of Aquatic Plants

Another important component to pond filtration is the use of plants. Many gardeners add a pond to their landscape for the variety of aquatic plants available, and while their beauty is certainly an aesthetic asset; a critical benefit is the work these plants do to help filter the water. Plants help purify pond water by reducing nutrients, filtering out sediments, and absorbing toxic compounds through the process of phytoremediation.

If these excess nutrients are not removed, algae will feed on them, resulting in green water, string algae, or both. Algae control is not the only way plants help create a low-maintenance ecosystem pond. Submerged and marginal plants also provide food, shade, and protection for the fish and other wildlife that live in and around the pond.

Low-Maintenance Customers

To keep pond water quality high, the simple process of repeatedly turning the water over through the mechanical and biological filters by way of the pond pump is needed in order to create a naturally balanced, low-maintenance ecosystem pond.  Add the remaining components of plants, fish, aeration, rock, and gravel, and you’ll find greater success in creating easy-to-maintain water features for both you and your customers.

To learn more about creating a naturally balanced pond, take our FREE “Introduction to Pond Ecology” online class at Aquascape University.

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