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Aimed primarily at beginners to the hobby, this series of articles will take you step by step through the process of understanding how a good koi pond works.
Part 10: Water
This month’s subject is an overview of water and water quality. What is water, what are water parameters and which are important?
What is water?
In scientific language water is known as H2O which is a chemist’s shorthand way of saying that it consists of two atoms of a gas called hydrogen joined together with a single atom of another gas called oxygen to make one molecule of the liquid we know as water.
The way these two gasses stick together to form water is another subject that is far too complicated to explain in a koi keeping magazine. But it is this “stickiness” that allows water to support aquatic life and is the fundamental principle behind all the water parameters we measure to ensure our pond water is suitable for koi.
When these atoms stick together there is a little bit of the “glue” left over and the molecule of water remains slightly sticky. Other atoms or molecules can go into a body of water and remain stuck there. We call that dissolving.
Water is called a universal solvent because of the wide range of other chemicals and gasses that will dissolve in it. Arguably the most important gas that will dissolve in water is oxygen because this gas is very important to life. Some clever bacteria can live without oxygen but no complex life such as plants, animals or fish could live without it. If oxygen couldn’t dissolve in water, life could exist on dry land but nothing could live underwater and so koi and other fish simply couldn’t exist.
Whilst oxygen may be a vitally important gas that will dissolve into water, it isn’t the only gas or chemical that will dissolve and have an important effect on what life can thrive or even just about survive in any particular body of water.
A simple example is salt. Salt easily dissolves in water and, with a few exceptions, fresh water fish cannot live in strongly salted water such as sea water and marine fish cannot live in fresh water. Water parameters that suit some fish may not suit others.
Stepping away from water quality for a moment but on a closely related subject which is currently topical is the subject of salt in koi ponds. Don’t put salt into a koi pond because you have been told “it will be a tonic that will do them good after the winter”. Salt is a very useful medicinal treatment but, where-ever possible, it should be used outside the pond as a short term salt bath or as a medium term treatment in a hospital or quarantine tank, not as a long term treatment in a koi pond. Carp have evolved to live in fresh water, not salt water. Their osmoregulatory system can cope with salt in the short or medium term and sometimes the benefits of salt as a medicinal treatment outweigh its disadvantages but salt isn’t the natural environment for koi.
Water Parameters
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A typical manual test kit
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If different gasses or chemicals can dissolve in water and either be a benefit or otherwise to the fish living in it, we need a way to establish what is in a body of water in order to see whether it is suitable for them. Looking at the water just isn’t enough. Many chemicals, regardless of whether they are beneficial or harmful, are invisible when dissolved and this makes it impossible to judge the water quality by sight alone. What is needed is a way to measure the chemical properties of water and produce readings that tell us what is dissolved in it.
Test kits and electronic meters are the usual way to take these measurements and the values they indicate are called water parameters. I sometimes measure several water parameters to give me specific information about water but, while all tests can provide valuable information, I only regard six out of all the available tests as being crucial. One of these six tests, in my opinion, is more important than the other five. Before you read which one I think is the most important at the end of this article, see if you can guess which one it is.
How electronic meters and test kits work
Some water parameters can be measured by the purely electronic means of passing an electric current through the sample and measuring what happens or by measuring the electrical voltage generated by the water itself. Typical examples are a TDS meter (total dissolved solids) or a pH meter. These are the exceptions.
Most electronic test meters and most manual test kits are based on the principle that some chemicals will produce a colour change in the sample to which they are added according to a particular parameter such as its pH. Other chemicals produce a colour change that will indicate other water parameters such as, if there is ammonia in the sample. In this case it is the degree of colour change that will determine the level of ammonia in it.
Chemicals that are added to a sample to produce these colour changes are called reagents. With manual test kits, the resulting colour of the sample can be compared to the colour chart supplied with the kit to see which colour is the nearest match as shown in figure 1.
Where an electronic meter is used, similar reagents are added to the sample to produce colour changes. The degree of change is measured inside the meter simply by shining a light through the sample and measuring how much light passes through it before the reagent is added and again after the reagent has produced the colour change. See figures 2 and 3. Electronic arithmetic inside the meter calculates the difference between the two values of light that can pass through the sample before and after the change and puts the appropriate value of the parameter on the display. It’s as easy as that. And you thought that electronic photometers were complicated!
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Figure 1: Light that can pass through sample is measured before reagents are added
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Figure 2: Light that can pass through sample is measured again after reagents have been added and had time to develop
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Six important tests
Remembering back to part 1 and the discussion on the necessity for biological filtration, I described the major pollutant in a koi pond as being ammonia. This ammonia is produced as a waste product as a result of koi digesting and metabolising protein. Protein contains amino acids and amino acids are so called because they are chemical compounds that contain ammonia. It is during metabolism of protein that the ammonia is released and excreted.
The ammonia bug (nitrosomonas) has evolved to utilise waste ammonia from its immediate environment. In a biological filter, it doesn’t do this as a favour to koi keepers; it uses the ammonia, not exactly as a food, but as a means of producing sufficient chemical energy to take in carbon from the water. This carbon is used to build new cell material so that it can grow and divide to make more nitrosomonas bugs.
Ammonia in the aquatic environment is a naturally occurring pollutant because it is continually being excreted by fish, and bacterial action cannot remove it instantaneously. This means that the ammonia level in a natural lake or koi pond can never be true zero and so very low background concentrations are tolerated by koi and other fish.
In a pond, koi will also tolerate short term small rises in ammonia level in situations such as where the biological filter of an unheated pond comes out of its winter dormancy because this is exactly what happens in the natural environment. As temperatures rise in spring, the fish that have spent the winter months conserving their energy at the bottom of a lake become more active and begin feeding which increases their ammonia excretions. The naturally occurring bacteria which have been dormant in the winter then slowly begin to become active and recommence the nitrogen cycle. This delay between the fish beginning to feed and when the natural bacterial colony reaches full efficiency results in a short period where ammonia levels rise above the normal low background level and fish have evolved to tolerate these short term rises.
So, whilst it is normal for there to always be a very low background level of ammonia and for it to increase slightly in unheated ponds in spring, the ammonia level is an important water parameter to monitor. Although in a koi pond there always will be small variations, if the level is allowed to rise above a low background level and remain there for any length of time it will cause harm to the koi in that pond.
After the ammonia bug has utilised ammonia to build cell tissue, it excretes its own waste product – nitrite. Nitrite is also toxic to fish but fortunately, a second bacterium, the nitrite bug (nitrobacter) has evolved to take advantage of this free source of energy. As with the ammonia bug, it doesn’t actually use nitrite as a food, it uses the chemical energy that allows it to take in carbon from its environment and build cell tissue in the same way as the ammonia bug does with ammonia. After this process, the nitrite bug excretes its own waste product - nitrate.
There are bacteria that exist in nature that can utilise nitrate, but for conventional biological filtration in koi ponds, the process whereby fish excrete ammonia which is then turned, firstly into nitrite and then into nitrate, stops just there. The ammonia has gone and ultimately has been replaced by nitrate which accumulates in the pond and stays there unless diluted by water changes. This means that if the ammonia level is regularly tested along with the nitrite level, the major risk to koi from pollutants can be monitored. Although far less dangerous to koi than either ammonia or nitrite, I always suggest that the nitrate level is also tested at the same time.
Predicting the future
The results of these three tests can be compared and will, not only give a great deal of information about the present efficiency or health of the bacterial colonies in the biological filter, but if taken regularly these three parameters can predict the future. By comparing the results of these three tests against each other and with those taken previously, small changes or trends in the test results, will give advanced warning if something is beginning to go wrong. Corrective action can then be taken to prevent these warning signs from turning into a full-blown filter failure. This will be discussed in detail next month when the individual water tests and what the results can tell us are examined.
In addition to ammonia nitrite and nitrate, there are three other tests that I consider important. The description of the way nitrifying bugs use either ammonia or nitrate as an energy source to allow them to take carbon from the water provides a clue to one of them. KH is an important test because it is a measure of carbonate in the water which is a major source of the carbon that the bugs need during the nitrogen cycle. Firstly, they could not remove either ammonia or nitrite without it so if ever the KH should fall to zero, biological filtration would come to an abrupt halt. Secondly, something disastrous would happen, the pH would drop like a stone, possibly to a level that would quickly kill the koi. The KH level and pH are two more parameters that can predict a future disaster in time for us to take avoiding action.
Oxygen is the sixth important water parameter. Koi cannot live without it but it is one that I rarely test with my oxygen meter, or test kit!
If the answer to the earlier question; “which is the most important water parameter in koi ponds?” is pH, and if oxygen is a vital water parameter, but one which I rarely test with a meter or test kit, I will close this part with two more questions: Why is pH the most important parameter and why do I rarely check pond oxygen levels with a test kit or meter? Answers next month.
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