What is a good Ammonia level for Freshwater Fish?

Ammonia is one of the few chemicals that play an equally important role in both freshwater and marine aquariums. However, there are common misconceptions about the sources of ammonia, its nature, and its toxicity.

In a well-established reef aquarium, the problem of high levels of NH₃ usually does not occur, because the vast number of bacteria and algae present contributes to the rapid removal of ammonia from the water. Against the background of low oxygen levels, ammonia can become the leading cause of aquarium death. When something in the aquarium dies, NH₃ is released as a result of rotting; increased levels of ammonia can lead to other organisms.

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Sources of Ammonia in an Aquarium

The primary source of NH₃ in the aquarium is fish and other organisms that feed on organic substances.

Fish produce ammonia in large quantities through their gills, and possibly in small amounts with their urine. Therefore, any aquarium should have mechanisms that prevent NH₃ concentration from rising to a toxic level.

Heterotrophic bacteria can also become a source of significant amounts of NH₃ in the aquarium. For example, uneaten fish food that has been broken down due to exposure to bacteria will also become a source of an NH₃ release.

Many organisms in aquariums also emit ammonia, such as crabs and shrimp. Almost all the inhabitants of a coral aquarium emit a certain amount of NH₃.

The reason for the release of NH₃ by such organisms is that with organic food, they consume significantly more nitrogen, which is required for the construction of new tissues. Accordingly, they have to somehow remove excess nitrogen. The usual method of removing nitrogen is via NH₃, along with urea and some other nitrogen compounds.

Other sources of NH₃ are tap water (mainly if it contains chloramine and has not been treated with ion-exchange resins), impurities in sea salt, and other additives.

Also, the high content of ammonia can be the result of contamination of calcium or magnesium chlorides, while NH₃ appears as a result of technological processes in the production of salt. Calcium and magnesium supplements can be a significant source of NH₃, especially when aquarium owners try to save money and use cheap sources of calcium or magnesium chloride.

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Toxicity of Ammonia

Ammonia is toxic to fish. NH₃ can cause damage to the gills, which leads to impaired gas exchange, ion regulation, and blood pH regulation.

The results of its influence can also be a complicated transfer of oxygen to the tissues, causing metabolic disorders and effects on the nervous system, leading to hyperactivity, convulsions, and death.

Toxicity can be measured in various ways. One of the most common ways to measure acute toxicity is to measure the concentration that leads to the death of half of the organisms over a specified period. A time interval of 96 hours is usually used.

Another problematic point related to the toxicity of NH₃ is the ratio of free ammonia and ammonium ions. Although ammonium ions are also toxic to marine fish, they are still less toxic than free NH₃. The toxicity indicator usually takes into account only the concentration of free ammonia. Non-fatal levels of ammonia can also cause severe problems for fish. Accordingly, the task of aquarium owners is to keep the attention of ammonia significantly below the lethal level.

What level of Ammonia is safe for the Fish?

There is no safe level of ammonia; even the lowest level can be a problem. It is necessary to carry out checks and to determine the cause of the increase in the content of NH₃ as soon as possible and immediately take measures to remove it or at least dilute it.

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Reducing the level of Ammonia in the Aquarium

The way to solve the problem depends on its cause. It may take a little investigation to determine what went wrong. However, you need to start by replacing most of the water. You need to make sure the water topped up in the aquarium is free of chlorine and has the same composition and temperature.

Water substitution is a great way to reduce toxic levels of ammonia, especially in small-volume systems and in aquariums for fish treatment or for quarantine. 

As practice shows, the amount of NH₃ is usually reduced by about the fraction corresponding to the replaced volume of water, so changing 30% of the water volume will reduce the concentration of ammonia by 30%. However, if there is an ammonia-releasing source in the aquarium, the level of NH₃ will quickly increase again. In emergency situations, it is acceptable to change a larger volume of water.

If the level of ammonia continues to increase, it is necessary to monitor its level with a test kit and to keep replacing the water to maintain the concentration of NH₃ at a low level.

Ammonia is very toxic to fish and to other aquarium inhabitants. Although it is not usually necessary to measure the concentration of NH₃ in an established reef aquarium, this procedure is essential when keeping fish in temporary tanks such as transport packages and medical or quarantine aquariums.

Many aquarium owners associate ammonia with processes that are typical of a new aquarium. Before starting the original inhabitants, it is necessary to reduce the content of NH₃ to as low as possible.