How do NH4 and NH3 differ

What is ammonium / ammonia?

Ammonium (NH4) is an inorganic nitrogen compound that is created when bacteria break down proteins in the course of the nitrogen cycle - it is the first breakdown stage that is later further metabolized into nitrite and nitrate. Naturally, the ammonium value rises in the incoming aquarium - it is normal for an ammonium peak to occur here. As long as the aquarium is not yet populated with animals, this value does not matter. The substance is harmless to plants in the aquarium.

Depending on the pH value, ammonium changes to toxic ammonia (NH3) around. The proportion of ammonia increases with increasing pH. The ratio of NH is at a pH of 9.44 to NH3 at 1: 1, at a neutral pH value of 7.0 the ammonia content is approx. 1%.

1 ammonia content of the water

The following formula is used to calculate the ammonia content in the water:

However, it is certainly easier for non-mathematicians to read the value in the table below.

2 Ammonium / ammonia as a basic fertilizer

Ammonia is one of the most widely produced chemicals, it is the raw material for the production of other nitrogen compounds, and it is often used for the production of fertilizers - among other things it becomes urea (urea - CH4N2O) produced.

3 ammonia in nature

In nature, ammonia occurs as an intermediate product in the protein metabolism of humans and animals, but due to its toxicity it is quickly excreted or - as in humans - converted into the non-toxic urea (and then excreted). Bacteria are interested in ammonia: cyanobacteria, for example, can convert the nitrogen (N) from the air into ammonia (nitrogen fixation), which they then use to produce protein. Plants that are particularly rich in protein, such as beans, form a community with such nitrogen-fixing bacteria in order to obtain sufficient nitrogen for protein production.

4 Problems in the aquarium

Ammonia (NH3) acts as a strong cell poison, especially - but not only - in the nervous system. Ammonia can appear suddenly in the aquarium due to its dependence on the pH value. NH3/ NH4 On the one hand, it is released into the gills by the fish and other aquatic animals as digestive waste via sodium ammonium pumps, on the other hand, it is also produced in the aquarium when bacteria break down protein compounds.

4.1 High population in aquariums with a high pH value

Ammonia can occur in harmful doses especially if there is a high level of contamination (and thus a high level of protein excretion in the faeces) and the pH is clearly in the alkaline range, i.e. above 7.0. This can apply in a tap water aquarium with hard water, but also in the case of special water values ​​with a high pH value, as is the case with Malawi or Sulawesian aquariums. If the pH value of the aquarium is in the alkaline range, you should check the NH content4 / NH3 especially keep an eye on.

4.2 pH value increases

Sudden increases in pH are rare. However, they can occur, for example, when changing water. If the last water change was a while ago, or if the tap water has a correspondingly high pH value, or if you add calcareous material to soft, acidic water, the pH can skyrocket. At a pH of 7.0, only 1% of the total concentration (NH4 and NH3) in the form of ammonia. The higher the absolute ammonium content of the water, the more likely it is that ammonia will also become a problem.

5 Lethal dose of ammonia

5.1 fish

The fatal dose for fish is around 1 mg / l ammonia, for young animals the problems start much earlier: here, 0.2-0.3 mg / l are fatal. But even ammonia values ​​of around 0.03-0.05 mg / l, which are not immediately fatal, lead to severe chronic damage in fish. Animals from flowing water, such as trout, are particularly sensitive.

5.1.1 Symptoms in fish

With ammonia poisoning, the fish hang on the surface of the water, breathing hard and gasp desperately for air. Their color becomes pale. Some fish also lie down on the bottom or shoot through the water in a panic.

5.2 prawns

In the case of shrimp, the relatively low value of 0.2 mg / l ammonia is deadly toxic. Stream shrimp in particular, such as the bee shrimp, have an even lower tolerance to the neurotoxin.

5.2.1 Symptoms in shrimp

If the ammonia concentration in the aquarium water is too high, the shrimp twitch, they fall over and die.

6 measures

6.1 Immediate action to change water

As with many aquarium problems, the number one measure for ammonia poisoning is a generous water change. This dilutes the ammonia in the water. If necessary, repeat until the animals in the aquarium no longer show any symptoms of poisoning.

6.2 Finding causes

Possible causes for a permanently increased ammonium / ammonia content are:

  • Decomposition processes (particularly often: food lying around in the aquarium)
  • Overfeeding
  • too high stocking
  • Fertilizers not suitable for the aquarium
  • Soil substrate (Plant Soil)
  • fertile soil

If the high ammonia value is caused by pre-fertilized soil, frequent water changes are carried out until the values ​​normalize. Depending on the setup, this can take about 8 weeks or longer.

A nutrient medium can also release ammonium later, especially if spots develop. If the ammonium levels in the water are permanently elevated, it should therefore be removed as a precaution.

7 Prevention through plant growth

Ammonium is a good source of nutrients for the plants in the aquarium, NH4 supplies nitrogen and is particularly readily absorbed by plants. In a properly planted aquarium with good vegetation and healthy plants, ammonium / ammonia is used directly as it occurs - this means that critical concentrations cannot arise in the first place. In particular, heavy-hungry and fast-growing plants such as waterweed, hornwort or mermaid ensure that this nutrient is quickly removed. In addition to a well-functioning biological filter, healthy plants are the number one prevention against ammonia problems in the aquarium.


author: Ricardo Castellanos
Co-author: Ulli Bauer

photos: Table and formula: Ricardo Castellanos