Koi are ammonia factories
Although koi are easily the most attractive and endearing of fish,
when it comes to hygiene they are not quite so appealing! In fact they
are incredibly mucky, often called ‘water pigs'. Their size and
insatiable appetite, together with the typical stocking levels of most
ponds, means that copious amounts of waste are produced every day,
especially in summertime. In the huge expanse of a large lake, this
isn't a problem but the situation is markedly different in the confines
of the average pond. Left alone they would quickly pollute the pond and
end up poisoning themselves with their own waste! Maintaining good,
clean water is the most important task for all koi-keepers, as even low
levels of pollution can have serious consequences for the fish.
The control of nitrogenous wastes such as ammonia and nitrite is
vital, as these products can be harmful in even minute amounts. Luckily,
Mother Nature, in the shape of nitrifying bacteria, provides a helping
hand by breaking down these toxic wastes into less harmful products.
This takes place in the nitrogen cycle, a natural phenomenon of crucial
importance to koi-keeping. The nitrogen cycle is at the heart of the
biological filters used by most hobbyists and it goes without saying
that an understanding of the nitrogen cycle is essential if water
quality problems are to be avoided. To develop a full understanding we
need to appreciate the relationship between nitrogenous compounds, fish
stocking levels, feeding and filtration. Then we can understand how
water quality problems arise and how to rectify them before they become
Organic material usually contains proteins in variable amounts. When
proteins are broken down, either by bacterial decomposition or as a
waste product of protein metabolism, ammonia is formed. Bacterial action
converts ammonia, which is extremely toxic, into less toxic nitrite,
which in turn is converted to nitrate, a relatively harmless substance.
This process of converting ammonia into nitrate is called nitrification.
It all sounds great but there is potential for problems lurking in every
pond if something goes wrong!
The main source of ammonia in koi ponds is fish metabolism.
Metabolism is a general term covering all the various processes taking
place in living organisms, such as food digestion, energy production,
tissue repair and cell growth. During this process, complex food
structures are broken down into simple amino acids (from proteins),
carbohydrates and fats and reformed according to the fish's needs. Any
surplus is stored as body fat or excreted as waste. Excess amino acids
cannot be stored and end up being converted to ammonia in a process
called deamination and then excreted into the water via the gills. Any
undigested food is passed out with the faeces. This process is not
exclusive to fish, indeed all animals produce metabolic ammonia.
However, in most animals ammonia is immediately converted into a less
toxic substance, usually urea, and excreted in the urine.
In the case of fish, Mother Nature decided that the large volumes of
water in oceans, lakes and rivers would adequately dilute the harmful
ammonia - but obviously no one told her about koi ponds! Koi, being
voracious eaters, produce large amounts of ammonia and may be considered
as ammonia factories, converting
expensive fish food into ammonia and other wastes. The amount of ammonia
produced is directly related to the amount of food given each day, which
of course depends on the stocking level and size of fish.
Further sources of ammonia are decomposing fish wastes, undigested
fish food and other organic matter. When such matter decomposes, it is
broken down by bacterial and fungal action into simple compounds. This
process is called mineralisation. A whole host of organic products,
including ammonia, are produced during decomposition, which is why
rotting matter always smells so awful.
A natural difference
A good starting point in understanding the nitrogen cycle is to
appreciate the difference between a natural environment, such as a lake
or river, and a managed closed environment typical of the average pond.
In nature, free nitrogenous compounds such as ammonia, nitrite and
nitrate are extremely scarce, except where waterways are polluted by
farming activities or sewage works.
The nitrate produced during nitrification is a superb plant food
which plants, including algae, use to form plant proteins. Plants are
then eaten by fish and other herbivores who convert the plant protein
into animal protein. Predation by carnivores on the herbivores then
passes nitrogen, in the form of protein, up the food-chain. When plants
or aquatic animals die their protein is decomposed and released as
ammonia to start the cycle over again.
The Nitrogen Cycle
The important point is that, in a natural system, no extra nitrogen
in the form of fish food is being introduced so virtually all the
available nitrogen is 'locked away' as plant or animal protein.
Therefore high levels of ammonia, nitrite or nitrate are extremely rare.
When we consider a koi pond we see a marked difference in both
stocking levels and feeding regimes, both of which combine to produce
substantial amounts of ammonia. The volumes of water in a koi pond are
quite minute when compared to a large lake so there is far less dilution
nitrogenous compounds. The other main difference is the lack of plant
life in the average koi pond. Algae, which produces 'green water', and
blanketweed are actively discouraged by koi keepers, leading to very
little nitrogen being converted into plant protein. The end result is
that free nitrogenous compounds are common in koi ponds - in stark
contrast to what one finds in nature.