How to Use Aquatic Plants As Biofilters for a Small Fish Pond

A biofilter is usually a separate tank full of aquatic plants that filter pond water. Pond fish are known as "dirty fish" and produce a lot of nitrogen. The nitrogen compounds, ammonia and nitrate, can become toxic to fish especially when ammonia levels rise. Plants absorb the fish waste, purifying the ammonia from the water and keeping the fish healthy. Once the water has gone through the filter, it is purified and sent back into the pond.

Things You'll Need

  • PVC pipes
  • Pond pump
  • Plastic strips
  • Screen material (such as milk/bread crate and hardware screen)
  • Bulkhead fittings
  • Aquarium-safe silicone adhesive
  • Sediment
  • Aquatic plants
  • Powerdrill
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Instructions

    • 1

      Calculate the size of the filter tank, which should be 10 percent of the pond size. For example, a small 100 gallon pond would need a 10 gallon filter tank. Any waterproof container can be used.

    • 2

      A bottom flow chamber needs to be at the bottom few inches of the container. Using an aquarium-safe silicone adhesive, glue wide strips of plastic, such as acrylic, that are a few inches high to the side of the container. These will act as support columns.

    • 3

      Use he plastic strips from Step 2 as column supports to hold up a screen that will be used to separate the sediment and plants from the bottom flow chamber. Make a screen with a bread crate or milk crate (cut to the size of the filter container) and cover with hardware screen. Set this on top of the plastic strip supports.

    • 4

      The filter's intake water should flow to the bottom flow chamber, so the plants can adequately absorb the fish waste. Cut holes every few inches into a PVC pipe and cap the end of the pipe. To feed the water to the bottom of the filter, use a bulkhead fitting and place the tube in through to the bottom of the container, under the screen.

    • 5

      Put down a layer of sediment and rocks on top of the screen for the plants to root in.

    • 6

      Fit a PVC outflow back to the pond near the top of the filter container.

    • 7

      Add the plants to the filter container. Fast growing leafy plants are the best for filtration purposes. Floating plants require less maintenance and can be placed directly in the pond, but do not remove as many toxins from the water.

    • 8

      Clean the filter and prune the plant roots once every few months.