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Roger's Aquatics Pages |
This is a biological process where bacteria convert Ammonia to Nitrite and Nitrite to Nitrate. It is important because both Ammonia and Nitrite are highly toxic to fish. Nitrate is also toxic but only at high concentrations.
The bacteria that carry out this process are Nitrosomonas and Nitrobacter. These belong to the group of bacteria known as Obligate Chemoautotrophs (or sometimes Chemolithotroph). What does this mean? Like most scientific terms it is made up from Latin or Greek roots.
Chemo = Chemical
Auto = Self
Troph = to feed.
So they are Chemical Self Feeding, probably the easiest way to explain is that plants are Photoautotrophs – note that the only difference is that the Chemo root is replaced by Photo (or Light). So plants are Light Self Feeding. A plant uses light energy to convert Carbon Dioxide and Water to carbohydrate and Oxygen. A Chemoautotroph uses Chemical Energy to convert Carbon Dioxide and Water to Carbohydrate and Oxygen.
The other part of the name is Obligate – this is in it is normal sense – these bacteria are Obliged to live that way, they cannot use anything else as food. So Nitrosomonas, which converts Ammonia to Nitrite must have a source of Ammonia as food or it will starve to death. Many people think that you must leave filters slightly dirty "to feed the bacteria". Well leaving the dirt in place does feed bacteria, but not the ones you want. Nitrosomonas and Nitrobacter can live in a perfectly clean environment with just a supply of chemicals.
These reaction requires large quantities of both ammonia and oxygen. The result is that these bacteria grow very slowly by bacteria standards. Many bacteria will divide every 20-30 minutes. Even in optimal conditions Nitrosomonas only divides every 7 hours, and frequently it may only divide every few days. Nitrobacter is even slower.
The other thing you need to know is that these bacteria do not live free in the water, but stick to a substrate. This can be anything, the aquarium glass, gravel, plants and rocks are all colonised, but the bacteria grow slowly in this sort of environment because they are relying on water currents to bring them Oxygen and "food" (Ammonia or Nitrite). They also colonise the filters, here they do much better because the filter pump is continually brining them a fresh supply of water together with Oxygen and a fresh supply ofood.
This is a very unusual bacteria. Nitrosomonas uses Oxygen to convert Ammonia to Hydrogen Ions, Nitrite and Water. This is the reaction that occurs when ammonia burns in air. It uses the energy this creates to fix carbon into Carbohydrates
Carbon Dioxide Water are combined to give Carbohydrate and Oxygen. No Oxygen is given off as it takes more Oxygen to burn the ammonia than is given off by the fixing of the carbon dioxide.
These bacteria carry out the second stage of the conversion - Nitrite plus Oxygen gives you Nitrate. The energy produced is used to fix Carbon in the same way that Nitrosomonas does/