What is a good ammonia level for freshwater fish?

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  • Updated on: 17/04/2020

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 toxicity.

In a well-established reef aquarium, the problem of high levels of ammonia usually does not occur, because the huge 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 main cause of aquarium death. When something in the aquarium dies, ammonia is released as a result of rotting; increased levels of ammonia can lead to the death of other organisms.

what is a good ammonia level for freshwater fish@seagul / Pixabay

Sources of ammonia in an aquarium

The main source of ammonia 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 the concentration of ammonia from rising to a toxic level.

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

Many organisms in aquariums also emit ammonia, such as crabs and shrimp. Almost all the inhabitants of an aquarium with coral, which in the course of their life consume food, emit a certain amount of ammonia. 

The reason for the release of ammonia 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 ammonia, along with urea and some other nitrogen compounds.

Other sources of ammonia are tap water (especially 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 ammonia appears as a result of technological processes in the production of salt. Calcium and magnesium supplements can be a significant source of ammonia, especially when aquarium owners are trying to save money and use cheap sources of calcium or magnesium chlorides.

what-is-a-good-ammonia-level-for-freshwater-fish@huyphan2602 on Unsplash

Toxicity of ammonia

Ammonia is toxic to fish. Ammonia 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 difficult transfer of oxygen to the tissues, causing metabolic disorders and effects on the nervous system, which can lead 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 certain period of time. A time interval of 96 hours is usually used.

Another difficult point related to the toxicity of ammonia is the ratio of the amount of free ammonia and ammonium ions. Although ammonium ions are also toxic to marine fish, they are still less toxic than free ammonia. The toxicity indicator usually takes into account only the concentration of free ammonia. Non-fatal levels of ammonia can also cause serious problems for fish. Accordingly, the task of aquarium owners is to keep the concentration 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 ammonia as soon as possible and immediately take measures to remove it or at least dilute it.

what is a good ammonia level for freshwater fish@ezphoto / FreePik

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 exactly what went wrong. However, you need to start by replacing most of the water. You also 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 ammonia 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 concentration of ammonia 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 continue to replace the water to maintain the concentration of ammonia 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 ammonia in an established reef aquarium, this procedure is very important 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. In this case, before starting new inhabitants, it is necessary to reduce the content of ammonia to as low as possible.

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