Alan’s Book

Chapter 5 Ammonia

Ammonia is highly toxic to fish.

Ammonia exists in two forms, NH3 (unionised and toxic) and NH4 (ionised and less toxic). Both pH and temperature determines the proportion of NH3 and NH4 in a particular water sample.

Lower proportions of toxic NH3 are present in an ammonia sample which has a low pH (more hydrogen ions) and low temperature.

Higher proportions of toxic NH3 are present in an ammonia sample which has a high pH (less hydrogen ions) and a higher temperature.

pH Water temperature

5C 10C 15C 20C 25C

6.5 50 33.3 22.2 15.4 11.1 Ammonia in ppm

7.0 16.7 10.5 7.4 5.0 3.6

7.5 5.1 3.4 2.3 1.6 1.2

8.0 1.6 1.1 0.7 0.5 0.4

8.5 0.5 0.4 0.3 0.2 0.1

9.0 0.2 0.1 0.09 0.07 0.05

Table showing the level of ammonia at a range of pH and temperature values that maintain unionised ammonia at levels considered to be relatively non toxic.

The above table indicates that at pH of 6.5 and a temperature of 10C ammonia remains in its less toxic state up to values of 33.3 ppm.

Understanding the toxicity of ammonia with respect to temperature and pH can prove useful if the pond system has a “pH crash” (see chapter 16 for a full explanation).

A pH crash can occur at any temperature, especially when frequent water changes are omitted or if rainwater is used as a top up supply for the pond.

The indications from a pond water sample that a crash has occurred will be KH = 0 and ammonia = High! Some nitrite may be present but this is likely to be low in comparison to the ammonia content. The pH will be lower than 6.5.

The level of ammonia detected and the actual pH will depend upon the stocking levels and the lapsed time period between the drop in pH and its detection.

If a pH crash is not detected at an early stage, ammonia levels can rise substantially to the maximum values shown on conventional test kits (circa 8 ppm) and I have seen ponds where this ammonia level and a pH of 5.2 have been recorded.

These parameters need correcting as quickly as possible however caution is needed such that the pH is maintained at a useful, yet safe level of about 7.0 until the ammonia levels reduce.

Reducing the ammonia levels by dilution (water changes) and keeping the pH just high enough by the addition of sodium bicarbonate to allow the bacteria to reduce the ammonia too, will ensure that the ammonia remains in the less toxic ammonium form.

pH crashes can be avoided by suitable pond design and management; such problems are common in koi ponds and account for major and totally unnecessary losses of koi.

Increasing the pH to a level of 7.0 will reduce the stress to the koi associated with maintaining their body fluids at the correct level which is approximately 7.4.

Where does the ammonia come from?

Terrestrial mammals dispose of their nitrogenous waste (ammonia) in urine via the kidneys; fish excrete ammonia in the same way, as well as continuously via their gills.

Faecal matter and uneaten food are converted to ammonia by bacteria in a process known as mineralisation; both faecal matter and uneaten food are deposited directly into the pond water.

In contrast to mammals, fish use the same environment as a toilet as they do for a dining room!!

It follows that the more fish we keep in a given body of water, the higher the level of waste and ammonia will be in that water.

Our filters are in reality sewerage systems for koi ponds!

As fish keepers we are fortunate that Mother Nature has arranged things such that once a food source is available, suitable organisms will multiply in response to the food source and use it for their own needs, thus reducing its presence in the environment. This is the case with ammonia in a body of water such as a koi pond where bacteria and other organisms grow in response to the food source provided by the ammonia and process it ammonia to less toxic forms. The correct conditions of pH and other parameters are necessary for this process.

The bacteria which use the ammonia also use oxygen from the water during what is known as the “Nitrogen Cycle” where ammonia is reduced to nitrite and then to nitrate. During this process they use oxygen and release carbon dioxide into the water as a by product of their metabolism.

During the period when the filter is establishing its bacterial population it is probable that high ammonia levels will be detected. As any detectable level of ammonia would be considered too high it is difficult to give precise danger levels as the pH and temperature of the pond water affects the toxicity of the ammonia.

It is worth noting that ammonia is more toxic at high pH and temperatures.

Ammonia is extremely toxic to koi, and gill, and even brain damage can occur if exposure is prolonged. It is because of this fact that it is preferable to establish bacterial colonies in a pond system capable of dealing with the nitrogen cycle before any fish are introduced. This is explained later in the chapter which deals with filtration.

The bacteria which process ammonia are relatively fast growing and robust; due to this ammonia levels are usually reduced fairly quickly providing conditions of pH, alkalinity and oxygen are suitable.

Testing for ammonia in your koi pond

Ammonia is measured as TAN (total ammonia nitrogen)

The ammonia content of a water sample can be measured in a variety of ways as follows;

1) Liquid test kits where drops of a reagent are added to a measured amount of water to be tested and the value of the ammonia is determined by the colour of the sample when compared with a colour card provided with the test kit.

2) An electronic test meter with a test probe which when inserted into a water sample will give a reading of the ammonia level value on an LCD screen.

3) Please note that chloramines in a water sample may read as ammonia!

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