Now although the fish and plants go a long way to helping the health of the pond, there is almost always the need for a little bit more help, in the form of a bio-filter. Bio-filters are basically filters that use bacteria to clean the wastes out of the water. These bacteria feed off the excess nutrients in the water, small algae particles, rotting plant and animal material, etc. It is a very environmentally friendly alternative to chemicals that many people add to the water to try to do the same job. Bio-filters can either be purchased ready to go, or you can make them yourself using a bucket with lid, some special material inside the bucket, and a pump to circulate the water through. This special material is simply a porous, non-dissolving material, which the water passes over and through. The little particles of impurities get caught on the surface and in the little pores of this material, and this is where the bacteria grow and multiply, eating the nutrients and particles, hence cleaning them out of the water. The water that then comes out of the filter is free of little impurities, and enters the pond as filtered water.

As you can see from the picture, the water enters the bucket from the top, and flows through a piece of gauze, which catches any larger particles, like leaves, etc. It then flows over the porous material, which can be anything porous, but I usually use zeolite, or scoria. Scoria is the preferred rock, as it is easily attainable through landscape yards, or hardware stores, and for the small amounts needed for a filter, is relatively inexpensive. Zeolite is another form of porous rock, but is more expensive. At the end of the day, it only needs to be porous for the bacteria to grow, and for the nutrients to be easily trapped. Once the water has passed through the scoria, it is then either passed over bio-balls (one bucket filters) or flows into a second bucket, which is full of bio-balls (two bucket filters). The function of these bio-balls is simply again to create a surface for the bacteria to live on and eat the impurities. This second batch of bacteria eats the impurities missed by the first lot. You can buy ready made bio-balls at a good aquarium shop, or you can make your own (and why not? Lets promote self-sufficiency) out of cut up bits of poly pipe (refer picture).

The most important thing to remember with regards to the filter is that the bacteria need the water to survive, so the pump that feeds the filter must be on 24 hours a day. If it is turned off for longer than about 6 hours, the bacteria will die, and the filter will not work until the bacteria have re-multiplied, and this can take up to about six weeks. And where do the new bacteria come from? Well, once again you can buy the bacteria in bottles from good aquarium shops, or you can put several fish in the pond and let the bacteria breed naturally from the fish waste. Why spend a lot of money buying the bacteria when it gets there on its own anyway? My pond is large, and it was going to cost me approximately $150 to buy the bacteria, so I just waited about six weeks, and they were in the filter and functioning all by themselves (isn’t nature wonderful??). Avoid at all costs adding something to nature artificially. Bio-filters are natural because the bacteria in them are naturally occurring; you are just providing a medium for them to grow on. In a natural waterway, these bacteria would be on the rocks where the water tumbles over them, or on the rocks in the water. Natural waterways are cleaned using the same bacteria.

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Last modified: 14/03/08