Different types of filters for your koi pond include:
Although they have fallen out of favor in recent time owing to exhaustive maintenance demands, undergravel filters are the most reliable and effective mens of keeping the water in your koi's pond clean and healthy. The concept is easy, a grid of perforated pipe under a deep (12-18 inch) bed of fine gravel draws the water down through the gravel whigh traps suspended solids and provides vast surface area for colonization of beneficial bacteria. James' koi pond uses an undergravel filter in addition to a pressurized sand filter.
Swimming pool sand filters are also very effective ind becoming more and more popular with koi enthusiasts today owing mostly to their ease of operation. They are however expensive to operate since they require a high pressure pump which consumes a large amount of electricity. The water from backwashing the filter makes excellent fertilizer for the garden.
Gravity fed multichamber filters are the current state of the art technology in filtration. The pump required to return the water to the pond only has to develop enough pressure to raise the water to the top of the pond or waterfall and are therefore very economical to run. in the past, multichamber filters were constructed on sit of concrete and were very expensive to build. Today there are a few manufacturers of fiberglass filters making them a smart choice.
The pump fed and gravity returned box filter is the best way to filter small ponds (less than 2000 gallons). They are cheap to buy, cheap to operate , easy to maintain and are available through almost any mail order or online aquarium or pond supplier as well as at many nurseries that cater to the water garden market.