How nitrite gets into aquarium water

nitrification

Nitrification is the conversion of ammonium and ammonia by bacteria into nitrite.

Fish release ammonium and ammonia into the aquarium water as part of their metabolism. A certain group of bacteria called Nitrosomonas convert ammonium or ammonia into nitrite. Another group of bacteria, the so-called Nitrobacter, convert the resulting nitrite into nitrate.

Nitrosomonas

A new aquarium has relatively few bacteria that convert ammonium and ammonia into nitrite. In the first few days and weeks, these Nitrosomonas must multiply so much that they convert the ammonium and ammonia that the fish later produce into nitrite as quickly and completely as possible.

Nitrobacter

As soon as there is nitrite in the water, the second group of bacteria also multiplies, converting the nitrite further into nitrate. These Nitrobacter need about 2 weeks until they have multiplied accordingly. In the meantime, more nitrite is produced than is converted. The nitrite level in the aquarium is constantly increasing. The so-called nitrite peak occurs. Only when there are so many Nitrobacter in the aquarium that more nitrite is broken down than new is produced, does the nitrite peak gradually decrease.

Ammonia and nitrite are toxic.

Ammonia and nitrite are toxic to fish. Therefore, fish should only be placed in an aquarium when the initial nitrite peak has passed.

The bacteria live in the filter.

Nitrosomonas and Nitrobacter prefer to settle in fine-pored materials such as foam mats, Siporax, etc.

Lower nitrite level

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Detailed instructions on how to lower nitrite levels can be found here. The quickest measure against increased nitrite levels are several large water changes. If the nitrite levels are deadly high, about 80% of the water can be changed several times a day.

The nitrite value can only be permanently reduced to a safe level if the fish stock is not too high and the filter is used. The running-in of the filter can be accelerated if old filter sludge from a run-in aquarium is placed in the new filter. If the mud has to be transported for more than an hour, the transport bag should be shaken from time to time.
If no filter sludge is available, bacterial concentrates from the trade can be used.

Feeding is reduced or, if possible, stopped completely until the nitrite value has fallen so that as little new nitrite as possible is produced.

Check nitrate test

Dipsticks and measuring liquids can show wrong values, e.g. B. are overaged. Some water is boiled for a quick check. The water vapor is allowed to condense on a clean plastic surface. With this water, the nitrite test must show a nitrite value of 0 because it is distilled water.

Nitrite peak in the aquarium

What is the nitrite peak?

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There are only a few bacteria in a newly set up aquarium. If organic substances, e.g. B. plants, fish and fish food, come into the aquarium, when they decay or as a result of their metabolism, ammonium and ammonia are released into the water. More ammonium is formed in acidic water and more ammonia in alkaline water. While ammonium is relatively harmless and consumed by plants as fertilizer, ammonia is very toxic.
Ammonia and ammonia are converted into nitrite, which is also toxic, by bacteria known as Nitrosomonas. Other bacteria, called Nitrobacter, convert the nitrite into nitrate. Plants use nitrate as fertilizer. Excess nitrate is removed from the aquarium with water changes.

In a newly set up aquarium, enough bacteria must have settled for these degradation processes to work effectively. The more food the bacteria get, the more they multiply.
The bacteria prefer to settle on the filter substrate and in the substrate. The nitrite-producing bacteria only multiply when sufficient ammonium and ammonia are present. The bacteria that produce nitrate only multiply when enough nitrite is available.
However, the development of Nitrobacter is increasingly inhibited the more the nitrite value rises above 1 mg/litre.

So, in a new aquarium, a certain amount of ammonium and ammonia accumulates first. When the Nitrosomonas have multiplied enough, they produce more and more nitrite until the ammonium and ammonia in the water becomes less and less. Since there are not enough Nitrobacter in the aquarium, the nitrite level in the water increases. This increase is called the nitrite peak. Due to the ever-improving food supply, the nitrobacter eventually also multiply. Since the cell division of the nitrobacter takes a relatively long time (one day), the nitrite value initially rises even faster than the multiplying bacteria can break down.

Over time, however, more and more nitrite is converted into nitrate, until finally the nitrite value slowly decreases. Over time, an equilibrium is formed in which as many pollutants are broken down as are newly created. For this, of course, there must be sufficiently large settlement areas for the bacteria.

Because in an aquarium without special precautions, nitrate is usually only consumed by the plants, the excess nitrate produced must be removed by changing the water. But there are also special nitrate filters in which nitrate is further converted. If excess nitrate remains in the aquarium, there is a risk that algae, which also use nitrate as a nutrient, will proliferate.

Nitrite is toxic to fish and many newly introduced fish die in newly established aquariums because of the nitrite peak. Therefore, a new aquarium must be broken in before fish are introduced. A new filter can be inoculated with filter sludge from an old aquarium so that it can be run in as quickly as possible, i.e. so that the necessary bacteria can multiply as quickly as possible. After the initial nitrite peak, only a few fish are used. The stocking is then slowly increased. The bacteria have to constantly adapt to the amount of pollutants to be broken down. Otherwise, too many pollutants can accumulate and cause disease or death among the fish.

How high is the nitrite peak?

How much nitrite is produced, how high the nitrite peak is and how long it lasts depends on how many fish are in the aquarium, how heavily fed, etc. When there are many fish and heavy feeding, the nitrite peak is high. With fewer fish and less feeding, the nitrite peak is lower. A concrete value cannot be given because too many factors influence the value. This also includes how many bacteria are in the aquarium at the beginning and how quickly they multiply due to the prevailing conditions.

The duration and height of the nitrite peak are influenced by

How long does the nitrite peak last?

As a rule, it is assumed that the nitrite peak will be over after a running-in period of approx. 4 weeks. Depending on the conditions, the peak can also occur after 8 or more weeks. There are also aquariums in which no nitrite peak was found after the new installation. With a safety factor, it is therefore advisable to place the first fish in a newly set up aquarium after 4 to 6 weeks.

With a nitrate test, regular measurements can be used to easily determine when the nitrite peak begins and when the peak ends.
After introducing new fish, the conditions in the aquarium change. More pollutants can then accumulate than were previously broken down by the bacteria. It is possible that the bacteria must first multiply again before the degradation capacity is high enough. So another, but usually smaller, peak can occur. If the trimming is slightly increased, the effect is hardly measurable. If the stocking is greatly increased, a strong peak can follow. It therefore makes sense to monitor the nitrite value for a while with tests, even if the stock changes.

Is the water changed during the running-in phase?

Arguments against water changes in the start-up phase

retract filters

There are enough bacteria in an established aquarium for most of the pollutants to be broken down. Some of the bacteria are also in the open water or are flushed out of the filter into the open water. When a new filter is connected to the aquarium, bacteria also get into the new filter. Over time, the system settles down so that there are as many bacteria in both filters as there is food, ie ammonia/ammonia and nitrite.

Dissociation equilibrium between ammonium and ammonia

The ratio between ammonium and ammonia depends on the pH value. Relatively more ammonium is present at low pH values, and relatively more ammonia is present at higher pH values. Ammonia is toxic.

The concentration of ammonia the fish can tolerate depends on the oxygen and carbon dioxide content in the water. The toxic effect is significantly increased when little oxygen or little carbon dioxide is present.

Ammonium is not, as is often written, non-toxic. For example, ammonium acts as a cytotoxin in most plants. In most plants, ammonium is therefore quickly converted into the amino acid glutamine.
But ammonium is at…