Q. In another issue of AFI you mentioned that it was possible to build a filtration system for a pond for around $30. Was that a misprint? Can you give me a list of materials and instructions?
A. No, it wasn’t a misprint. There are perhaps dozens of filter designs available for small ponds that can be bought or built for around $30 — not including the pump. Commercial examples include the foam-sleeve filters made by Danner Mfg. (the Supreme line) and the sponge filters offered by Tetra, among others.
A 20-gallon (76-liter) plastic pail plumbed with PVC pipe and filled with ½-inch (1.3-centimeter) gravel or lava rock will serve a pond of around 500 gallons (1893 liters) or so and cost about $30 (see accompanying diagram). It can be installed either inside or outside the pond. You can find the details of numerous designs discussed in publications such as KOI USA. A local koi, goldfish or pond club can provide a wealth of information on inexpensive but effective filters.