Page 27 - Koi Net - On-Line Koi Magazine - Issue 1

THE NITROGEN CYCLE is put into it, naturally occurring bacteria will soon be
Syd Mitchell explains
As protein in food is metabolised the waste product,
ammonia, is excreted mainly through the gills along with
carbon dioxide which is the waste product from normal
respiration.
Koi, in common with all fish, excrete ammonia as a
waste product. This is a perfectly natural process and
results from them needing protein in their diets. There
are various forms of protein but all forms have one thing
in common, they are made from substances called
amino acids and amino acids are compounds based on
ammonia.
When protein is digested and metabolised, the
ammonia compounds in it become a waste product and
must be excreted. The majority of the ammonia, (up to
around 90%), that is excreted by koi is expelled through
the gills as part of the normal respiration cycle.
Fortunately nitrifying bacteria have evolved to make use
of the waste products of fish as a free energy resource
and they will helpfully remove it for us. There are two
main species of bug that are particularly suitable to do
this in the pond environment. The ammonia bug
(nitrosomonas) which will convert the ammonia into
nitrite, and the nitrite bug (nitrobacter) which will convert
that nitrite into nitrate. Neither does this as a favour to
koi keepers, but if we make them a suitable home in our
filter system, they will use these pollutants as an energy
source that allows them to take up carbon from the
surrounding water in order to grow and to multiply. In
doing so, they remove ammonia and convert it into
nitrate which is far less harmful to koi and it is for this
reason that biological filtration is a necessary part of the
pond filtration system.
The natural maturation process
These bacteria are prolific in nature so if a pond is filled
with new dechlorinated water and koi or any form of
aquatic life that excretes ammonia as its waste product
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present in the water. They are primarily soil bacteria so
they literally blow into new sources of water on specks
of dust blown by the wind and they are also present in
the faeces of fish.
Pond ammonia, nitrite and
nitrate levels as a biofilter Colonies nearly mature slowly
matures in the presence of increase feed rate to normal
fish. The actual time it takes
for the filter to mature will Nitrobacter growing, 3
vary depending upon the reduce feeding
temperature and the quantity Nitrosomonas growing,
of food given to the fish. feed sparingly 2
1
Ammonia
Nitrite
Nitrate
In view of that, the usual way to start up a biofilter is to
provide a suitable media in a well aerated bay then
release a small number of koi into the pond and wait.
The fish should be fed very lightly until the biofilter
matures so that they will only excrete a small amount of
ammonia into the water. As soon as the first ammonia
bug gets into the system it will begin to use the rising
level of ammonia and start to multiply.
At first, the relatively small numbers of bugs that begin
to populate the media will be unable to cope with all
the ammonia from even a small number of small fish
even if they are being fed very little so ammonia levels
will begin to rise as shown by the red ammonia curve in
the diagram.
As more and more ammonia is converted to nitrite by
the ammonia bugs, this will become the energy source
for the second colony of bacteria, the nitrite bug.
Remember that these use nitrite as their energy source
to allow them to take the carbon they need from their
environment in order to grow and to multiply.
Chemically, there is far less energy available in nitrite
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