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Testing water     (Testing Water)


I wrote the following articles for Koi Magazine.
Therefore they own the copyright but the Editor has given permission for them to be republished here.

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Testing Water - Part 1

“No! I’m sure there’s nothing wrong with the water - it’s not green, it’s crystal clear.”

That was the answer I was given when I suggested to a koi keeper that the continuous health problems her koi were experiencing might be due to poor water quality. So is that it then?  Clear water, good; green water, bad.  If it were true, this article would end here and the Editor would have to find something else to fill the next few pages.

Testing Water
Clearly it isn’t true, many substances that are commonly found in pond water, and which are harmful to fish, are colourless. Also, some koi keepers prefer green water because they believe that it promotes good skin quality and colouration. (See Algae: clean versus green, in issue 121).
[Algae: clean versus green, was published in Koi magazine; issue 121 June 2008]

If we cannot tell whether water is good or bad by it’s colour, how can we tell?
One way to find out is by using a manual test kit. Simply take a sample of the pond water, add a chemical to it that will change colour if, say, ammonia is present, and look for the colour change.  In this case, the deeper the colour, the more ammonia is present. Compare the sample to a colour chart, and read the number alongside the matching colour to find the level of ammonia in the sample.  Chemicals that are added to a sample to cause this colour change are called “reagents”.  There are many different types of reagent, each of which can give us different information about what is dissolved in the sample.  Taken together, these tests will give a complete picture of what is, or is not, in the pond.


Top Tips testing water What should be in the sample?
If you supposed that the answer to this question should be: - “Absolutely nothing apart from the water itself”, you would be wrong.  koi, in a pond full of chemically pure water, would immediately be gasping at the surface for air and would soon die - chemically pure water contains no free oxygen for them to breathe.

How about:- “Nothing but water and some oxygen?” Well, that would give the koi the absolute minimum requirements for an unhappy pond where they had a short, miserable life.  It would be even shorter if there was no method for removing the ammonia that koi (and fish, in general) excrete continuously.

The usual way to remove ammonia is by means of a biological filter, in which we set up a home for a couple of species of bacteria (nitrosomonas and nitrobacter).  The first of these bugs removes ammonia by “eating” it and excreting nitrite.  This is also toxic to fish. Fortunately the second species “eats” the nitrite, and excretes nitrate. The result of this biological activity is a build-up of nitrate in the water.

Hungry Bacteria
Bacteria don’t remove ammonia and nitrite from pond water as a favour to pond keepers. They use these chemicals, along with huge amounts of oxygen and carbonate, to make their cell tissue and multiply. In other words, they “eat”, they grow larger, then they divide into two and the process starts again.  These bacteria cannot just remove ammonia (or nitrite) without oxygen and carbonate as well; they need these in order to complete this process. Removing carbonate from the pond water, and the biological process itself, has a tendency to reduce the pH.

To ensure that we have a happy pond with healthy koi in it, we must make a few tests to ensure that the right chemicals are there, in the correct proportions, and that pollutants are within acceptable limits or parameters as they are known. Ensuring that these parameters are correct is the key to healthy fish.


Post it testing water 1Six parameters
Taking stock of the parameters covered so far, it is important to know that there is sufficient oxygen for both fish and filter bacteria. These bacteria control levels of ammonia, nitrite and nitrate which must not exceed acceptable limits.  There must also be sufficient carbonate for the bacteria or they cannot function as we would wish. Also, insufficient carbonate will allow the pH to fall.  That makes six parameters in all that can be tested to give sufficient basic information to ensure that the fish will be kept in a good environment. How many of these tests are necessary? The answer is, all of them, but since I do not like making unnecessary work for myself, there is one test that I rarely make by using a test kit.


Testing for oxygen
Accurate oxygen tests can be fiddly and time consuming.  Simple tests are not always accurate. Every time I look at my pond, I see air pouring into it from a large flat ceramic air diffuser and there is also a small waterfall.  When I look into my filter bays, I see so much air being fed to the aerated K1 bay that the K1 is almost jumping out of the water (I call it my airborne K1 bay).  The pond isn’t overstocked and it is clean, so whenever I have tested the oxygen level, it is always at “saturation point”. This means it is at the maximum value that it could be, and it could not go any higher even if more air were to be added.  Under these conditions I consider it unnecessary to test for dissolved oxygen with a test kit, I can see that the fish are getting plenty of oxygen, every time I walk past. This should not be interpreted as: - “Don’t bother about checking dissolved oxygen”, but as: - “There is no need to test what is obvious every time you look at your pond”.

Temperature oC








Oxygen mg/L








Saturation values of oxygen in fresh water at sea level
(Maximum level of oxygen a pond can hold)

If a pond is really well aerated, these six tests can be reduced to five; ammonia, nitrite, nitrate, carbonate and pH. The first three parameters are self-explanatory. They obviously are a measure of how much ammonia, nitrite or nitrate is in the water. The concepts of pH and the carbonate parameter, which is usually referred to as KH are much more complicated.

pH scale GIF resizedScience alert!
pH is always written as; small “p” capital “H” even when it is put at the beginning of a sentence or paragraph, as I have just done. There are no exceptions! It is a way of measuring acidity or alkalinity, and it was first named pH by a Danish scientist called Sørensen after the German expression potenz hydrogen.  There is no direct English translation, but it is generally considered that the term “power of hydrogen” is near enough.  For koi keepers who do not wish to become involved in chemistry, just remember this: - “pH is a measure of acidity or alkalinity.  It is measured on a scale of 0 to 14, where 0 is a strong acid, 7 is neutral, and 14 is a strong alkali”

The carbonate parameter is usually called carbonate hardness or KH.  It may seem odd that KH is used to represent carbonate hardness, but it is an abbreviation of karbonathärte which, in German, literally means carbonate hardness.  It is a measure of how much carbonate (or bicarbonate) is in the water. It can be measured in two main ways; degrees KH, or mg/L.


Post it testing waterDifferent names
On the continent of Europe, they generally prefer the expression mg/L which stands for milligrams per Litre.  Since there are one million milligrams in one Litre, this is exactly the same as ppm which was the old British way of measuring chemical concentrations or levels.  Another way, is to measure KH in degrees of hardness. One degree of hardness is equal to 17.848 mg/L, 2 degrees of hardness = 35.696 mg/L and so on. Confusing! It is further complicated because you will often see in old books, or whilst surfing the Internet, references to odH dKH,or oGH.  These are entirely different ways of measuring carbonate hardness and only add confusion to what is already a difficult subject to understand. My advice to those trying to understand what testing for KH is all about, is to choose to measure it in mg/L and then stick to that system when measuring other parameters. That way you will be measuring all your water parameters, except pH, with the same system of units and life will be less complicated.

Part two of this article will cover how to use standard test kits, what the results mean, what they should be, and how to take corrective action when necessary.

Make sure you buy next month’s issue to complete this essential water quality lesson.


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