5.2. Safe Ammonia Levels

We are going to predicate this article with a warning:

The ammonia level per the API test should always be 0.25 or lower, not because ammonia is that toxic, but rather because any ammonia indicates poor biofiltration which will kill fish from excess bacteria in the water.

If one has a new aquarium under four months old and one sees an increase in ammonia above 0.25 ppm per the liquid tests like API, this is generally nothing to worry about. Random ammonia spikes happen all the time with new aquarium setups. But if the increase is still there a week later, there is something wrong in the biofiltration of the aquarium and it needs to be addressed. To understand this better go to this link:

5.2.3. Ammonia Spikes (links to aquariumscience.org)

Ammonia in the Aquarium

Fish excrete ammonia gas across the gill membrane to rid themselves of nitrogenous waste. “Ammonia” in water exists in two forms:  un-ionized ammonia gas dissolved in water (NH3) and ammonium ions (NH4+). Un-ionized gaseous ammonia is toxic to fish at very low levels, while ionized ammonium is relatively harmless. The ratio of the two types of ammonia in water is directly related to the water pH and temperature. As pH decreases so does the portion of the ammonia that is in the toxic, un-ionized gaseous form. 

The popular API test measures BOTH the ammonia gas and the ammonium ion. This is called “total ammonia nitrogen”, TAN or ammonia+ammonium. So one needs to look at the pH of the water when trying to determine the toxicity of ammonia as measured by the API test. The toxicity of total ammonia is ten times greater at a pH of 8.0 than it is at a pH of 7.0. This relationship is the source of a great deal of confusion in the hobby. Over and over one will hear “ammonia kills at anything over 1 ppm“. And this simply isn’t true IF one is talking about the API ammonia+ammonium test results.

Lethrinops Red Cap Itungi
Lethrinops Red Cap Itungi

Toxicity of Ammonia

The most accurate way to illustrate the toxicity of ammonia is a chart derived from the University of Florida ammonia toxicity chart (Publication #FA16, “Ammonia in Aquatic Systems”, Ruth Francis-Floyd).

pH of the waterAPI Ammonia test in ppm
pHAlertAlarmToxic
6.61664160
6.81144110
7.083280
7.252050
7.431230
7.62820
7.81410
8.00.838
8.20.626
8.40.424
8.60.2512

To read the ammonia+ammonium levels on this chart find the pH of the aquarium first. Then find that pH in the left column. Read across as to the levels the API ammonia+ammonium tests will show. Green is the “Alert” level where increased testing is called for. Yellow is the “Alarm” level where one should do a 50% water change. And “Toxic” is the level where one should do at least a 75% water change. Note many of these levels require diluting the aquarium water with 9 parts of distilled water. Test the diluted water. Multiply the results by ten and you have the levels in the aquarium.

These numbers will shock most hobbyists but these numbers are confirmed by many research papers by many universities so they are solid. Note that this is also per Seachem, who many hobbyists seem to think is the most knowledgeable supplier in the world. 

Having said that one SHOULD keep ammonia+ammonium at the “undetectable level”, not because of ammonia+ammonium toxicity, but rather because it is an indicator of the health of the aquarium. Note that the API ammonia+ammonium test will measure 0.25 ppm (very light green) even with distilled water.

So “undetectable level” actually means equal to or less than 0.25 ammonia+ammonium as measured by the API test. An aquarium which has ammonia+ammonium at an “undetectable level” is probably a healthy aquarium with low bacterial counts.  Low bacterial count is always the chief goal in aquarium water. Low ammonia+ammonium and low bacteria count typically go hand in hand in any established aquarium.

This toxicity of ammonia+ammonium is supported by a host of references from the aquaculture farmers. They are raising fish for profit and sickly or dead fish aren’t profitable. So their research tends to be very accurate. This research can be found at the following link:

5.2.1. Ammonia Toxicity in Depth (links to aquariumscience.org)

tropical fish photo Geophagus altifrons
Geophagus altifrons

Ammonia Myths

There are some common misconceptions about ammonia+ammonium poisoning. One is that a malfunctioning automatic vacation fish feeder killed a bunch of fish through ammonia+ammonium poisoning. It wasn’t the ammonia+ammonium from the excess food that killed the fish. It was the bacteria and the bacterial toxins produced by the rotting food that killed the fish.

Many common bacteria (Streptococci and Clostridium to name two) produce toxins. These bacteria can reproduce rapidly. When some human eats spoiled meat and dies, death is not from the ammonia, death is from bacteria and bacterial toxins. The excess food rots and produces the bacteria and the bacterial toxins. The same holds true for when a fish dies and decomposes in an aquarium.

tropical fish photo Rocio octofasciata, Electric Blue Jack Dempsey
Rocio octofasciata, Electric Blue Jack Dempsey

Many think ammonia toxicity is manifested by red patches on the skin. This is not true. The first sign of high ammonia is mad dashing of the fish around the tank. The fish sense the high ammonia and are trying desperately to get out of the bad water. With very high levels of ammonia the internal organs start to bleed and a dark maroon patch can be seen in the belly. Only VERY high levels of ammonia result in red patches on the skin. Most red patches on the skin are bacterial hemorrhagic septicemia, not ammonia poisoning.

Ammonia in More Depth

There are some aquarium hobbyists who are interested in delving deep into the science and the calculations behind all aspects of the hobby. For those who are so inclined the following is pertinent:

5.2.1. Ammonia in Depth (links to aquariumscience.org)

5.2.3. Ammonia Spikes (links to aquariumscience.org)


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Translated in dutch by : Joost Abrahams
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