For a fish hobbyist, one of the most important pieces of equipment to have is a water filter. It's only natural that since your Koi will be living in your garden pond permanently (unless you sell them), you should go to all lengths to keep the water as clean and as debris-free as possible. In fact, it's even more important for a pond to have a properly-sized Koi filter because it's located outdoors.
Unfiltered Koi water will attain high concentrations of ammonia (excreted by the fish) and will turn green and foul-smelling before you know it. Toxic nitrates will build up and all sorts of foreign matter will find themselves on the pond surface over a short period of time - dead insects, sticks and leaves, uneaten fish food and other debris.
There are two components to Koi filters - mechanical filtration, which removes pollutants and debris physically, and the biological filter which converts ammonia and nitrates into less toxic substances. Both these stages help make life more comfortable and less stressful for your expensive pets. Remember that a happy Koi makes for a healthy Koi.
In mechanical filtration, dirt and other foreign matter is filtered with the use of pads, sand or beads which trap the pollutants so they can be taken out of the water easily. Water is sucked through the filters with the use of a pump. The pump's capacity to process water has a lot to do in how effective it will be. Experts say a water pump has to be able to handle at least 1/3 of the Koi pond's total capacity randomly. There are two kinds of pumps for Koi ponds, submersible pumps and re-circulating pumps. The latter are more effective for large ponds because of their durability and power although they can be quite noisy.
The cleaning process that happens in biological filtration is a bit more complicated. Noxious elements that have formed from pollutant and excretions from the fish like ammonia are acted on by bacteria which transform it into nitrates. Nitrates are still toxic to the fish, but anaerobic bacteria, again through the same process of biological filtration, convert them into nitrites which are not as dangerous to the Koi.
To make sure your fish are swimming in really safe waters, a drainage hole in should be built in the lowest part of the pond. Here, dirt can be sucked-out by the pump and trapped in the filter chambers. This along with an adequate aerator can be the perfect accompaniment to your Koi filter, making the water in your garden pond a clean and hazard-free habitat in which you can enjoy and take care of your fish for many years to come.