Homemade Filter

How to Build an Inexpensive Filter for a Garden Pond

By Marilyn Miller

This filter has had several versions over the years, but the current version is the most effective and easy to manage in that it is light enough to be pulled out of the pond by one person and needs little attention during the summer months. It services up to a 1400 gallon garden pond that is stocked with lilies and several varieties of goldfish. The filter can go into the pond in spring when the water temperature is around 55 degrees and be removed in the fall when the water temperature drops to the same level or it can be left in the pond over the winter if you continue to run your pump. The filter should be cleaned and the air conditioning filter material replaced annually.

The filter provides both mechanical and biological filtration. The air conditioning filter material helps keep debris from reaching the pump and the lava rock acts as a habitat for good bacteria providing biological filtration.


Materials for building the filter The materials needed to construct the filter are a plastic file crate, 2 sheets of plastic biodegradeable blue or green air conditioner filter material and some lava rock. The crate can be purchased almost anywhere. The furnace filter material is available at Wal-Mart, Lowes, and other places that sell air conditioning filters. Be sure to buy BIODEGRADEABLE filter material, not fiber glass.


Furnace material cut to fit crate Cut the furnace filter to fit the crate. The bottom piece will be slightly smaller than the top piece. The top piece needs to rest on the rails designed to hold the file hangers, so it will be an inch or so wider than the bottom piece. Rinse the filter material in water to remove any dust.

Rinse the lava rock to remove the red dust.


Crate lined with filter material Line bottom of crate with lava rock

Add pump Place the bottom and side pieces of filter material in the crate. Cover the bottom of the crate with a layer of lava rock. Place pump in crate. Use scissors to make holes in the filter material just big enough to allow the cord and discharge hose to be pulled through. Pull cord through it's hole and attach discharge hose to pump through it's hole. Fill crate with lava rock covering the pump. Place cover on top and tuck in so it fits snugly inside the top of the crate.

Fill with lava rock Finished filter


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