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What is the Nitrogen Cycle - As explained by Tom Lansing With the new season approaching and in light of the cold winter we
have had and may continue to have, I thought this article might really
One of the most important aspects of successful koi keeping or any fish keeping for that matter, is biological filtration and its function in the nitrogen cycle. I read recently, that the number one reason novice fish keepers become disillusioned with the hobby is the frequency in which they experience high death rates of their aquatic pets after setting up a new system. Statistically, as much as 75% of the fish sold to hobbyists will die within the first 30 days and 2 out of every 3 new hobbyist abandon the hobby within the first year. This data applies to all types of fish but nonetheless, they’re pretty staggering statistics. My very first four koi died in less than 24 hours. For some unknown reason to me at the time, they didn’t like all that chlorine I had in the water to keep it clear. One of the most common reason for these kill rates is known as ‘new tank syndrome’ or as your questioned asked, the ‘nitrogen cycle.’ The fish are simply poisoned by high levels of ammonia (NH3) that is produced by the bacterial mineralization of fish wastes, excess food, the decomposition of animal and plant tissues and let’s not forget, the additional ammonia that is excreted directly into the water by the fish themselves. The effects of ammonia poisoning in fish include: extensive damage to tissues, especially the gills and kidney; physiological imbalances; impaired growth; decreased resistance to disease, and; death. Nitrite poisoning inhibits the uptake of oxygen by red blood cells. Known as brown blood disease, the hemoglobin in red blood cells is converted to methemoglobin. This problem is much more severe in fresh water fish than in other marine organisms and can easily cause death. So, to quickly answer the question these are the ‘nitrifying bacteria.’
You don’t have to go any further but for those interested, here’s some additional information/data that I and few others might find interesting. Nitrifying bacteria are classified as obligate chemolithotrophs. This simply means that they must use inorganic salts as an energy source and generally cannot utilize organic materials. They must oxidize ammonia and nitrites for their energy needs and fix inorganic carbon dioxide (CO2) to fulfill their carbon requirements. They are largely non-motile (can’t move around easily) and must colonize a surface (gravel, sand, synthetic biomedia, and the 1001 other filter materials out there) for optimum growth. They secrete a sticky slime matrix, which they use to attach themselves. Species of Nitrosomonas and Nitrobacter are gram negative, mostly rod-shaped, microbes ranging between 0.6-4.0 microns in length. They have evolved to become extremely efficient at converting ammonia and nitrite. One disadvantage is, they have a very slow reproductive rate. Nitrifying bacteria reproduce by binary division. Under optimal conditions, Nitrosomonas may double every 7 hours and Nitrobacter every 13 hours. More realistically, they will double every 15-20 hours. Nitrobacter and Nitrosomonas bacteria have limited tolerance ranges and are individually sensitive to pH, dissolved oxygen levels, salt, temperature, and most chemicals. They cannot survive any drying process without killing the organism. Doc Conrad will disagree with the drying process part of that statement but until he supplies me with scientific data, non-anecdotal, science on this subject isn’t on his side. In water, they can survive short periods of adverse conditions by utilizing stored materials within the cell. When these materials are depleted, the bacteria die. There are several species of Nitrosomonas and Nitrobacter bacteria and many strains among those species. Most of the following information can be applied to species of Nitrosomonas and Nitrobacter in general., however, each strain may have specific tolerances to environmental factors and nutriment preferences not shared by other, very closely related, strains. This is why Genesyz (Lymnozyme) coexists with Nitrosomonas and Nitrobacter bacteria, they don’t compete for the same food source. Temperature The temperature for optimum growth of nitrifying bacteria is between 77-86° F (25-30° C). Growth rate is decreased by 50% at 64° F (18° C). Growth rate is decreased by 75% at 46-50° F. No activity will occur at 39° F (4° C) Nitrifying bacteria will die at 32° F (0° C). Nitrifying bacteria will die at 120° F (49° C) Nitrobacter is less tolerant of low temperatures than Nitrosomonas. In cold water systems, care must be taken to monitor the accumulation of nitrites. Here again, except for a few people I know that feel nitrifying bacteria can survive in freezing water, science isn’t on their side. If either of them has found some data to the contrary, I’d be most interested to see it. PH
Nitrosomonas growth is inhibited at a pH of 6.5. All nitrification is inhibited if the pH drops to 6.0 or less. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+ state. Dissolved Oxygen Maximum nitrification rates will exist if dissolved oxygen (DO) levels exceed 80% saturation. Nitrification will not occur if DO concentrations drop to 2.0 mg/l (ppm) or less. Nitrobacter is more strongly affected by low DO than NITROSOMONAS. All species of Nitrosomonas use ammonia (NH3) as an energy source during its conversion to nitrite (NO2). All species of Nitrobacter use nitrites for their energy source in oxidizing them to nitrate (NO3). Chlorine and Chloramines Before adding bacteria or fish to any aquarium or system, all chlorine must be completely neutralized. Residual chlorine or chloramines will kill Nitrifying bacteria. Most US cities now treat their drinking water with chloramines. Chloramines are more stable than chlorine. It is advisable to test for chlorine with an inexpensive test kit. If you are unsure whether your water has been treated with chloramine, test for ammonia after neutralizing the chlorine. You can also call your local water treatment facility. The type of chloramines formed is dependent on pH. Most of it exists as either monochloramine (NH2Cl) or dichloramine (NHCl2). They are made by adding ammonia to chlorinated water. Commercial chlorine reducing chemicals, such as sodium thiosulfate (Na2S2O2) break the chlorine/ammonia bond. Chlorine (Cl) is reduced to the harmless chloride ion. Since dichloramine has two chlorine molecules, a double dose of a chlorine remover, such as sodium thiosulfate, is recommended. Each molecule of chloramine that is reduced will produce one molecule of ammonia. If the chloramine concentration is 2 ppm then your pond will start out with 2 ppm of ammonia. Chlorine Remover will reduce up to 2 ppm of chlorine at recommended dosages. During the warmer months chlorine levels may exceed 2 ppm. A double dose would be required to effectively eliminate the excess chlorine. There’s a character (I mean that in a kind way) in the UK, who believes that adding DO (dissolved oxygen) to one’s filtration media is not only wrong, but has disadvantages. He’s the only person on the face of the earth that thinks that, as far as I’ve ever found. Actually, as I stated above, the nitrifying bacteria consume more oxygen then our fish require. I believe that this person feels that given your pond water is oxygenated well, there is enough left over for the nitrifying bacteria in your filters to use. I personally don’t want to have to depend on ‘left over’ oxygen for my nitrifying bacteria. Each one of my filter chambers has (4) air stones each, a total of 45 air stones. As to good books on aspects of koi keeping, in my biased opinion and tens of thousands of others, there is only one, ‘Koi Kichi’ by some relatively unknown British guy named Peter something. Good luck with your pond and filter system. Tom Lansing |
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