Page 80 - Koi Net - On-Line Koi Magazine - Issue 5

AMMONIA AND converted to nitrite, there will be more and more of their
NITRITE SPIKES
Why there can be an ammonia spike
followed by a nitrite spike in spring and
how to avoid it, Syd Mitchell explains
As I explained in previous articles, two species of
bugs are generally accepted to dominate in the nitrogen
cycle. The ones that convert ammonia to nitrite
(nitrosomonas) and those that convert nitrite to nitrate
(nitrobacter).
In pond water during summer, both species of bugs
multiply at a rate that balances the natural rate at which
some are ‘dying of old age’. The colonies of both
species soon achieve a stable size which is dictated by
their nutrient supply (ammonia or nitrite). In an unheated
pond during winter these bacteria do not actually die out
completely. The colony sizes will reduce somewhat
because the colder water causes the bugs to virtually
stop multiplying but the ‘death rate’ continues. (This
does not happen in a heated pond as the balance of
dying bacteria and the creation of new ones is
maintained.) So, in spring when the Koi are beginning to
regain their appetites, both species of bugs will have
reduced colony sizes and they will also multiply very
slowly whilst the water is still relatively cold.
We are all human, and when Koi that have hardly eaten,
if at all over winter, start to regain their appetites, the
temptation is to feed them as much as they will eat. This
temptation should be resisted or the sudden increase in
food fed to the Koi will produce high levels of ammonia
that the bug colonies will not be able to deal with
immediately. What will happen is that the first bunch of
bugs will have a feast on all that ammonia and will
multiply in number until all the ammonia is gone. In
doing so, their ‘waste’ product, nitrite, will be produced
in abundance.
During this time, the second bunch of bugs will initially
have had very little to ‘eat’. Then, as the ammonia is
80
nutrient available and they will also begin to multiply in
number until they have used it all. But they multiply at a
much slower rate, and so the conversion of this nitrite to
nitrate is much slower.
What this means in practice is that there is initially a high
ammonia spike which is fairly quickly converted to a
high nitrite spike, but it takes much longer for this nitrite
to be converted to nitrate and so it will persist for much
longer. A second problem with a high nitrite level is that,
if it gets too high, apart from the damage to your Koi, it
also will inhibit the rate at which bugs multiply. So it will
take even longer for the level to reduce, and your Koi will
be suffering for a much longer period.
One of the effects of high nitrite levels on Koi is that it
interferes with the way oxygen is carried around their
bodies. The nitrite combines with the haemoglobin in
their blood and changes it to methaemoglobin
(pronounced met-haemoglobin) which cannot transport
AVOID oxygen around their bodies. Because methaemoglobin
is brown, this will cause the gills to look brown instead
AMMONIA of ruby red. So a common name for nitrite poisoning is
AND NITRITE ‘brown blood disease’. In bad cases, Koi can suffocate,
even in highly aerated water.
SPIKES BY The safest way to avoid a high ammonia spike followed
by a prolonged nitrite spike is to feed the Koi very
FEEDING sparingly at first in spring. Test the water frequently, daily
SPARINGLY is not too often. There will be a sudden increase in
ammonia level. Reduce feeding even more and the
IN SPRING ammonia spike will reduce, but it will be replaced by an
increase in nitrite level. Keep feeding to a minimum until
this nitrite spike also reduces. Ammonia or nitrite levels
can be kept under control during this period by regular
10% - 20% water changes. It is sometimes said that
these water changes will slow down the rate at which
the biofilter matures, this is not true. As long as there is
a detectable level of ammonia or nitrite in the water, the
bugs will multiply to make use of the extra available
nutrient supply. The levels don’t need to be very high in
order to trigger them to multiply. If anything, high levels
of ammonia or nitrite are not only bad for Koi but, to
repeat the above, they also inhibit the rate at which the
bug colonies can grow.
81