Ammonia is one of several different forms of Nitrogen. The transition from one form of Nitrogen to another is commonly referred to as the Nitrogen Cycle.
Nitrogen is a requirement for life in all organisms because it is an essential part of RNA, DNA, and protein.
Nitrogen comprises over 75% of the atmosphere, but this huge reservoir is not usable by most organisms. It must be converted by lightning and nitrogen fixing bacteria.
This is the first of the five processes in the Nitrogen cycle--- fixation, uptake, mineralization, nitrification, and denitrification – and are all driven by microorganisms. For the purposes of this discussion, only the last two processes are of interest.
Nitrification is defined as- “The process by which bacteria in soil and water oxidize ammonia and ammonium ions and form nitrites and nitrates”.(The American Heritage® Science Dictionary).
The oxidation of ammonia into nitrites is accomplished by two genuses of bacteria, Nitrosomonas, primarily, and Nitrosococcus, to a lesser extent. Generally, their optimum temperature for growth is 30C/86F and the optimum pH is 7.5 – 8.0.
They have a relatively slow reproductive rate. Nitrifying bacteria reproduce by binary division. Under optimal conditions, Nitrosomonas may double every 7 hours. In the time that it takes a single Nitrosomonas cell to double in population, a single E. Coli bacterium would have produced a population exceeding 35 trillion cells.
Ammonia-oxidizing bacteria are also known to be unusually resistant to starvation conditions. Nitrosomonas europaea can immediately respond to the addition of ammonia after nearly one year of starvation.
It is commonly known that ammonia is toxic to, not only fish, but also other aquatic organisms. In water, ammonia exists in two forms – ionized (ammonium) and un-ionized (free ammonia). Ionized ammonia is, for the most part, harmless. It is the un-ionized form that is toxic and this toxicity is directly influenced by both pH and temperature with pH effecting the greater change. As pH (and temperature) rises, the toxicity of un-ionized ammonia rapidly increases.
Although 0.00 test results for total ammonia are possible and usually desired in a true Koi pond, it is both unrealistic and unnatural to strive for a complete absence of ammonia in an eco-system pond, but levels should never be allowed to reach toxicity. The following shows how Carp (Koi) may react to different levels of un-ionized ammonia (in mg/L).
0.00 is ideal. Values up up 0.019 might be tolerated for extended periods.
0.020 - 0.049 may be tolerated, but will cause long term harm
0.050 - .0.199 may be tolerated for a few days, harmful
0.200 - 0.499 May be tolerated for a day or two, very harmful
>0.500 Extremely Toxic, Fish should be moved to alternate location
(Koi and Water Garden Society of Central New York)
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