How to Make a Biological Pond Filter How to Make a Biological Pond Filter

The cheapest and easiest way to avoid ‘green water’ syndrome and maintain a healthy pond is by installing a biological pond filter. There are various commercial units out there on the market, but a pond bio filter is something you can create yourself once you understand the basic principle at work. Your homemade bio filter is a device that will provide a home for colonies of bacteria which feed on debris that finds its way into your pond. The debris normally includes the kind of stuff that turns your pond water green and cloudy. 

The Principle

A simple container such as a plastic toolbox, milk crate or grow pot can be utilized for this purpose. It should be at least a three to four gallon size and will need to house the biomedia – on which the bacteria already present in your pond will flourish - and a submersible pump. Biomedia can be almost any solid item such as stones or pebbles, gravel, plastic rings or balls, even hair curlers! The water is continuously pumped over the biomedia, enabling bacteria to go to work. This will then assist the nitrogen cycle to work efficiently, making available adequate amounts of oxygen and promoting a healthy environment for your fish and aquatic plants. 

To construct your biological pond filter you will need the following items: 

  • Container
  • Submersible pump
  • Open cell foam
  • Plastic rings, balls or hair curlers
  • Plastic piping
  • Drill
  • Knife or scissors
  • Mesh bag
  • Rocks, pebbles or gravel 

Step 1 – Foam the Container

Cut the foam into sections that will fit into the bottom of the container, plus each of the sides and the top. Make a hole in the top section of foam, large enough to pass the outlet pipe through. Cut another hole in the side section for the pump’s power cord. Line the bottom and sides of the container with the remaining sections of foam. This outer layer acts as the first stage of filtration and traps the larger particles and solid matter before water enters the chamber where the biomedia is stored. 

Step 2 – Add Biomedia and attach Pump

Put plastic balls, rings or hair curlers into the mesh bag and place in the bottom of the foam lined container. Then, following the manufacturer’s instructions, fit the plastic pipe to the pump. Place the pump on top of the plastic, with the inlet pipe facing the plastic and the outlet pipe emerging from the top of the container. Feed the pump’s power cord through the side hole in the foam lining of the container. 

Step 3 – Finishing Off

Fill the container with rocks or gravel, place the top section of foam to cover the opening and situate your biological pond filter at the bottom of your pond in a suitable location. You will need to remove larger debris such as leaves or twigs by hand using a skimmer and, twice a year, your bio filter will require cleaning. Simply wash out the container, biomedia and pump, then reassemble and replace.

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