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The Basics of Koi Pond Filtration (Page 3 of 3)



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Biological filtration, as the name implies, employs natural biological processes to convert the harmful wastes excreted by the koi and those produced by decaying plant matter in the pond into less invasive compounds.  Koi excrete ammonia, which is deadly to koi in large doses.  Certain anaerobic (non-oxygen-breathing) bacteria convert ammonia into nitrites, which are, unfortunately, also poisonous to koi.  The good thing is, there are 'good' aerobic (oxygen-breathing) bacteria that convert nitrites into nitrates, which are no longer deadly to koi.  These 'good' bacteria are also known as nitrifying bacteria.   Nitrifying bacteria occur freely in nature, and will populate your pond in time. 



Biological filters usually use bio-balls, sintered glass, porous rocks, ceramic rings, or synthetic high-surface area particles as filter media.  Biological filter media are designed to have as much surface area as possible for a given volume, in order to maximize the good bacteria population within the filters.  Since good bacteria are aerobic, special biological filters known as dry or trickle filters are becoming popular among koi enthusiasts.   A dry or trickle filter just lets the water 'trickle' down through the filter media in droplets before returning to the pond.  Trickle filters don't fill up with water, allowing the media to get highly oxygenated than water-filled biological filter chambers.  This gives the aerobic bacteria access to more oxygen.



Figure 4. Examples of various commercially

available filter media



Aside from the filters themselves, another equally important feature of a pond's filtration system is the bottom drain.  As its name implies, a bottom drain is a drain at the bottom of the pond where dirty water is sucked by the pump for transport to the filter chambers.  The bottom drain is normally placed at the center of the pond, and should be the lowest point on the pond bottom.  Thus, the entire pond bottom surface must slope towards the bottom drain.  A pond with no bottom drain will need frequent cleaning of its floor. Due to the importance of this feature, there are now many off-the-shelf bottom drains available in the market.



Figure 5.  Examples of bottom drains in the market




These are the basic filtration requirements of a koi pond.  A hobbyist can construct his or her own filters, or can simply buy off-the-shelf ones.  Sophisticated, easy-to-maintain filters are already widely available but be ready to spend some big bucks if you opt to go for these. 


By the way, ultraviolet lamp systems for killing algae may also be considered if green water is a persistent problem for you.  In fact, many koi experts consider the uv sterilizer as a 'must-have' item for successful koi keeping. These are usually placed before the mechanical filters since uv light makes dead algae clump together. I've had success designing filters that don't need uv light to keep the water clear though, so you may want to go for this as well.  Lastly, surface skimmers for removing wastes on the surface of the pond will also be required by your pond if you do see this problem during hot summer days.


Pond water quality is the key to enjoying your pond, so it is better to have a smaller pond with superb filtration capability than to have a large pond with undersized filters.



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See also: Trickle Filters







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