Ammonia; why do Koi produce so much of it?

Syd Mitchell's picture
Submitted by Syd Mitchell on Sun, 05/06/2018 - 09:37

By: Syd Mitchell

Even if you think you know all about Ammonia, you might just learn something new by reading this article!

Koi excrete ammonia into their pond because we feed it to them. We do this because Koi need protein in their diet - protein contains substances called amino acids and amino acids are compounds based on ammonia.  When protein is eaten and metabolised by fish, the compounds that were based on the ammonia molecule are converted back to ammonia and become a waste product which has to be excreted. It isn’t possible to put exact figures on the amount of ammonia that fish excrete because, apart from the huge variations in food available, the feeding regime makes a great deal of difference to how much food is fully digested and metabolised and how much is excreted in faeces after having been only partially digested.

Carp don’t have stomachs
Carp, in their natural habitat, will spend much of their day browsing for food and eating whatever they can find.  As a result, they have never needed to have stomachs.  Stomachs are only needed by fish or other animals that eat a significant amount at any one time.  These large amounts of food are initially broken down and stored in the stomach before being allowed to enter the intestines where the nutrients are metabolised. Since carp nibble at food all day, they don’t need stomachs to store a large amount of food that has been eaten in one meal until it can be digested later.  This means that they have never needed to evolve a stomach. Digestion takes place in the intestine, which is roughly twice the length of its body.

Enzymes which are used to break down protein are secreted along the intestine. If Koi are fed a great number of small feeds all throughout the day, virtually all, (if not all), of the protein in it will be metabolised. If Koi are fed large amounts less often, they will eat it because that is what they are genetically programmed to do, but as each larger amount travels through the intestine, there will be too much of it for the digestive enzymes and they won’t be able to completely metabolise the protein in it.

This fact, along with the different protein ingredients in Koi food, makes it difficult to make an exact science out of determining how much ammonia any particular Koi will excrete but we can calculate some guidelines if we assume an average Koi food and a feeding pattern that allows all the protein in it to be metabolised.

There is a scientific process called the Kjeldahl Analytical Method which can be used to determine the nitrogen content of any substance and, since ammonia contains nitrogen, this method can be used to calculate how much ammonia will be released from any particular Koi food after it has been completely metabolised.  Assuming a protein value of 40%, it can be estimated that 1 gm of an average Koi food with that protein content would produce about 40 mg of ammonia.

Bryant, Jauncey and Atack in their book on fish farming took this one stage further and, based on average feed rates, calculated that a guide to the quantity of ammonia that will be excreted by an active carp is 33 mg per hour per kilo of body weight.

What did that mean?
To simplify the science in the panel above, it means that a 1 kilogram Koi will excrete almost 800 mg of ammonia into its pond each day. This is obviously only an approximation because it is dependent on diet, feeding regimes and water temperature which will determine the level of activity and the amount of food that Koi will consume.

To simplify the situation one stage further, since Koi keepers tend to think more in terms of body length than body mass and few will have any experience of pure ammonia it may be easier to understand if we could stretch this example a little further by approximating body mass to length and if we also take into account that standard strength household ammonia is around 7.5%.  We could then say that an average 20 inch (50 cm) Koi, which will weigh about 2 kilograms, can excrete into its pond the equivalent of over a teaspoonful of standard strength household ammonia every 12 hours.

Clearly, this means that as long as there are fish in a pond there can never be zero ammonia in it.  There will always be some ammonia in the water because, no matter how fast is the turnover rate, it is impossible to instantaneously remove all that ammonia as quickly as it is being produced.

Zero ammonia cannot be achieved
The reason why many Koi keepers assume they have a zero ammonia level in their pond is that a common method of testing for it is by adding a few drops of reagent to a sample of the water and then comparing the colour of that sample by eye to the colours on a colour chart.  Test kits based on this method are simply not sensitive enough to show very low levels and so it is natural to assume that no noticeable colour change means that there isn’t any ammonia. In reality, there will always be a background level, even in a Koi pond with a high turnover rate and a very efficient biofilter.

If we have to accept that there will always be a background level of ammonia in our ponds, how high can this level be before it becomes harmful? There is no direct answer to this question, it all depends on that important parameter, pH

Ammonia and pH
When Koi excrete ammonia into their pond, it becomes one of two forms, free ammonia (NH3) and ionised ammonia (NH4).  The proportions of each of these two forms are dependent mainly on the pH of the water and, to a lesser extent on its temperature, but it is only the free ammonia that is really harmful. The ionised ammonia is far less so – approximately one hundred times less.

It is often said that ammonia is more toxic at higher levels of pH and temperature but this is a simplification. At lower pH and temperatures, very little of the ammonia in the pond is in the free ammonia form, and therefore there is far less of it to be toxic. As pH and temperatures increase, much more of the ammonia becomes free ammonia and so the toxic effects are greater.  Free ammonia is just as toxic at lower pH and temperatures; it’s just that there is far less of it.

Since carp and other fish have evolved in an environment where metabolising protein has resulted in them excreting ammonia as a waste product, they have evolved with ammonia as a natural pollutant in their lakes and waterways. They didn’t have fast turnovers of water through external filters; they just had the natural populations of the ammonia bug (nitrosomonas) and the nitrite bug (nitrobacter) which colonised every available surface in natural waterways.  These bugs could no more instantaneously remove all the ammonia as fast as it was produced than we are able to instantaneously remove ammonia with the same bugs housed in the filters we use today. This has resulted in carp, and other fish, evolving to have an inbuilt tolerance to ammonia provided the levels don’t become too high.

How much is too much?
Scientists working in the field of aquaculture have researched the effects of ammonia on fish. It was they who discovered that ionised ammonia (NH4) was almost non toxic and they also found that levels as high as 0.4 mg/L free ammonia (NH3) could be tolerated for periods of up to several weeks without ill effects but that, for long term exposure, levels below 0.02 mg/L were preferable since they would cause no harm no matter how long the exposure. As a result, although zero ammonia would be the ideal value to try to achieve in a pond, the researchers recognised that this isn’t possible in any practical situation, and it is now universally recognised that 0.02 mg/L is the maximum value of free ammonia that should exist, long term, in a fish pond or fresh water aquarium.

That would make understanding the ammonia parameter easy for Koi keepers – simply measure the free ammonia level in the pond and make sure that it never is allowed to rise above 0.02 mg/L.  Unfortunately it isn’t that easy, standard test kits and electronic meters cannot measure free ammonia because they cannot distinguish between the free ammonia and any non toxic ionised ammonia in the sample; they can only measure total ammonia which, as its name suggests, is the total of the two forms.

This is where the mathematicians stepped in and, since the proportions of free and total ammonia are dependent on pH and temperature, tables of values of pH versus ammonia were produced where total ammonia could be measured and the free ammonia component could be calculated with a slide rule. Slide rules had to be used because although these tables were published in 1979 and pocket calculators were invented in 1966, the first practical ones were not patented until 1974 so they were not in common use until very much later.

An easier table
Eventually, in 1992 the first widely published table that was easy for non-mathematicians to use was produced by OATA. Its simplicity lay in the fact that it removed the need to measure the total ammonia level and then calculate whether this was safe or not.  All the mathematical calculations have already been done so, by simply looking up the particular values of pH and temperature, the maximum allowable value of total ammonia for any system can be found.  It was designed to cover the full range of pH and temperatures that are found in ponds and aquaria of all types, not just Koi ponds. This wider range means that there is less room for detail in the area needed by Koi keepers.

With this in mind, I took the original scientific research and re-calculated a new table that gives the maximum allowable value for total ammonia in Koi ponds and quarantine tanks. By confining the table just to this range, it is possible to give greater detail in the area relevant to Koi keeping.

To use the table, look up the pond pH on the left, and its temperature at the top. The maximum allowable total ammonia (reminder; the value indicated by a test kit or meter), is shown where they intersect.  Whilst emphasising that as near zero ammonia as is possible always should be the aim, there will be occasions, such as where fish are introduced into new ponds where the biofilter isn’t yet mature and near zero values cannot be achieved.  This situation is called new pond syndrome and higher than ideal values of ammonia are the result.  There are other occasions where the ammonia level is higher than desirable and these elevated ammonia values are best controlled by zeolite or water changes but, as long as the values in the table aren’t exceeded, no harm will come to the Koi no matter how long this situation should exist.

Next month, the remaining two important water parameters, nitrite and nitrate, will be discussed and pH actually affects one of them.  This is only to a limited extent but is further proof of the importance of pH in a Koi pond. Can you guess which of the remaining two it affects?


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