This pond filter is easy to make and is lightweight. It will serve a pond of up to 1,400 gallons and may be used all year.
For this filter, get a plastic crate, blue or green biodegradable air conditioner filter material, a large aquarium pump and a bag of lava rock.
Cut the material to fit the inside of the crate. The filter material should fit along each side and the top and bottom. The bottom piece should be slightly smaller than the top piece.
After cutting, rinse the filter pieces to remove any dust. Rinse the lava rock to remove any dust as well.
Place the air filter material along the sides and bottom of the crate. Cover the bottom with a layer of rinsed lava rock.
Using a pair of sharp scissors, cut a small hole just large enough for the cord and discharge hose of the air pump. Place the pump at the bottom of the crate, on top of the lava rock.
Set up the pump by pulling the discharge hose and cord through the holes. Fill the crate the rest of the way up with lava rock, covering the pump.
Place the top piece of filter material on the crate, making sure it fits snugly at the top. Lower the filter into the pond.