homemade pond filter

Garden water features need filtration systems. For ponds with fish and plants, filtration is necessary to maintain a healthy ecosystem.

There are three general categories of filtration – mechanical, chemical, and biological. Some filtration occurs naturally in a circulating water feature. Usually, you need to supplement the naturally occurring filtration to some extent.

A well-balanced pond needs less supplemental filtration than a pond with too many fish or not enough plants. The right mix of fish, plants, and other pond creatures depends on the size and depth of your pond, your climate, and pond design (e.g., a waterfall and stream or a fountain sprayer.)

Mechanical filtration is a physical process and traps debris. Coarse filters include screens and strainers often built into pumps. Chemical filtration is done by adding processed minerals and chemical products to manage the pond ecosystem. A water feature with no fish or plants can rely on mechanical filtration such as screens and chemicals to keep the water clear.

However, if your pond contains fish and plants, restrict chemical filtration to water conditioners. Water conditioners remove chlorine from tap water. Many kinds of conditioners also neutralize some toxic metals and break the chlorine/ammonia bond of chloramines allowing neutralization of both toxins.

You must use conditioners whenever adding tap water to your pond. In addition to chlorine removal, water conditioners provide an added benefit. They improve the effectiveness of biological filters by helping bacteria attach to the filter media.

Biological filtration goes on in nature. It is a combination of mechanical and chemical filtration occurring when plants trap debris and sediment and then use the nutrients to grow and increase the amount of plant material sustaining the filtration process. It takes time to establish a balanced ecosystem in an artificial water feature.

Also, a truly balanced system is almost impossible to maintain all the time. This is because fish grow, plants die, organic matter falls into the pond, and temperatures change. All these factors can change the balance of the pond ecosystem. You can make your own biological filter that is easy to change as your pond changes.

Biological filters can be submerged in your pond or located outside the pond. If you locate your filter outside the pond, you must be sure that all connections and piping are watertight. A leak in an external filtration system will result in draining your pond. External filters can be tricky to build and size appropriately. Because of these intricacies and the potential for leaks, the biological filter below is intended for submersion in the pond.

A submerged biological filtration system is made of a few essential parts. First is a container to hold the media. Next is the media itself. Third is a pump to pull the water through the media. Fourth is the connections and piping for the system.

The container and media should be considered and decided on at the same time. The media needs to have a lot of surface area. This surface area is where beneficial bacteria will grow and work to clean the pond water. The media will also provide mechanical filtration by trapping debris.

Depending on the size of the openings for water to enter the filter, the strength of the pump, and the type of container, you may decide to include a screen or strainer as a pre-filter to prevent the larger debris from clogging the biological media.

The container needs to be big enough to hold the volume and weight of the media you pick. The media can be rocks or gravel, volcanic rock, plastic rings or balls designed to provide a maximum amount of surface area, plastic hair curlers, or small brushes.

Containers for gravel or rock need to be sturdy and rigid enough to hold the weight of the media such as a sturdy plastic pail or heavy-duty plastic planter. The containers for plastic balls or brushes and other lightweight media can be light and not have a lot of integrity such as a mesh bag or lightweight plastic jug.

For this filter system, the pump selected must be submersible. It must be large enough to pull water through the media. It must also be able to pump the water through the entire system if you are using it to feed a waterfall. The connection and piping need to be sized to fit the pump and media container. The outlet piping needs to support the pond design.

A simple biological filter used with a pump to feed a waterfall includes:

  • Pump
  • Plastic pail or planter
  • Mesh bag of porous ceramic cylinders
  • Medium size rocks
  • Connection for the pump to waterfall piping

To make the biological filter, punch several holes in the bottom and sides of the plastic container. Put the mesh bag of cylinders at the bottom of the container. Place the pump in the container with the inlet facing the cylinders and outlet piping coming out of the container.

Fill the rest of the container with rocks. Place the container in the bottom of the pond, either on its side or upright. Orientation for this filter system depends on the connection and type of the outlet piping, the depth of the pond, and the size of the container.

This type of biological filter system may only require cleaning once or twice a year depending on the fish and plant loading of your pond. Cleaning simply requires removal of the container from the pond and washing the rocks and cylinders.

To assure longer functioning of the filter between cleanings, size the container, and amount of the filter media as large as possible to still fit in your pond. Routine water testing will show when your filter needs cleaning.

A healthy pond does not need to be complicated or a lot of work. Nor does it need to be expensive. Try the filter system described here, or use the information to design one yourself, and see how little work a pond can need.

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