Article 3 - KOI Pond Filters -
Koi Pond Filters
Clear water in your Koi pond does not necessarily mean clean water,
it may contain colorless impurities, such as ammonia and nitrite,
that are harmful and can kill koi. Koi excrete urine and produce
faeces in the Koi pond, and ammonia is excreted through the gill
membranes. It is the job of the pond filter to remove waste from
the Koi pond which in the wild would be diluted by the large volume
of water or washed away by moving water.
Most pond filter media involved in maintaining a Koi pond have
a mechanical function. Settlement chambers allow gravity to drag
the solid waste out of the Koi pond 's water by slowing the water
flow. Such chambers usually come first in a filter. A vortex unit
provides greater settlement, the water in the Koi pond moves in
a circular movement allowing solids to gather in the centre where
they can be removed. In addition to baffle plates within the pond
filter which slow the incoming water, brushes or matting can be
used to strain the water of the Koi pond.
Biological filtration of the Koi pond relies on specific bacteria
to break down toxic waste products to less harmful substances. The
first stage is the breakdown of ammonia to nitrite in the Koi pond
by nitrifying bacteria, most important of which is Nitrosomonas.
The second stage is the conversion of nitrite to nitrate by Nitrobacter.
Both of these groups of bacteria are aerobic (need oxygen to live),
sediment building up in the Koi pond 's pond filter will deplete
the oxygen levels so it is important to keep sediment in the pond
filter to a minimum by having a settlement chamber first and by
cleaning the filter out occasionally (but not using tap water as
the chlorine will kill the bacteria).
A variety of different Koi pond filter media are available to put
in the filter, materials such as gravel, matting, hair rollers,
foam, and Canterbury spar are all suitable as they provide lots
of surfaces for the bacteria to live on.
A biological Koi pond filter will take weeks or months to mature
cultures of nitrifying bacteria are widely available and will speed
up the process. The process of Koi pond chemical filtration involved
activated carbon removing ammonia and other organic waste products
by adsorption, this means that the waste substances become linked
to the surface of the carbon. When the surface is 'full up' it has
to be replaced.
If a large Koi pond biological filter is present chemical filtration
should not be needed, but it is good to use while the biological
filter is maturing or isn't big enough for the pond. Some Koi pond
keepers use a sand filter as a final stage to 'polish' the water.
The Koi pond's water is passed under high pressure through sand
and comes out very clear, bacterial activity also takes place in
the sand filter. Sand filters are expensive though, and you can't
make one yourself because of the high pressure involved.
Biological filtration turns Koi pond's ammonia into nitrate which
is harmless to fish (unless at extremely high levels) but the disadvantage
of this is that algae love nitrate and you get an algal bloom. There
are two types of algae problems, green water and blanket weed. Green
water is caused by microscopic algae in the water, it is not harmful
to koi, actually it is beneficial, the koi eat the algae and it
enhances their colour, but you can't see them! Also in summer the
algae use oxygen and leave the Koi pond fish gasping. There are
various ways to get rid of the algae: a vegetable filter, plants
will use the nitrate so it is not available for the algae; an ultra
violet (UV) filter kills the algae as it passes through; algicide
chemicals can be used but the problem will just recur; magnets placed
on the filter pipe will disrupt algae cells internally, killing
them or preventing them reproducing. Blanket weed is filamentous
algae and forms long green strands, it is not really a problem,
it uses up nitrate and stops green water occurring, but it is unsightly.
Vegetable filtration, algicides and magnets will all work on blanket
weed, but UV filtration will not as the algae has to pass through
the filter to be killed and blanket weed is attached to the pond
Koi pond filters need to be cleaned occasionally to remove sediment,
take this into account when building one. Add a bottom drain to
each filter chamber so that sediment can be let out, it makes cleaning
much easier. Another thing that makes cleaning easier is to put
filter medium in net bags, not just pour it in all at once, as it
can then be more easily removed, one bag at a time.
One last important thing, never ever put tap water in a mature
filter, it will kill all the bacteria and you will have to let it
mature all over again.
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