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Understanding clay02         (Understanding Clay)


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

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Pond clay enthusiasts, are they just throwing handfuls of Japanese Dirt into their ponds?

All fish need minerals and trace elements in their diets.  Koi are no different in this respect. When a pond is first filled, it will contain minerals from the mains water supply unless they have been removed by a water purifier.  Any useful minerals will quickly be absorbed by the fish and by bacteria in the biological filter. Water changes and top ups will help to replace those minerals but the question is; will the mains water supply contain enough minerals and trace elements, and will these be the correct ones anyway?

....our average one kilogram koi on an average diet will excrete 33 mg of ammonia per hour

Just bacterial action alone uses huge quantities of carbonate from the water.  Koi excrete prodigious amounts of ammonia, and as we all know, ammonia is toxic so it must be removed from pond water.  Many different factors affect just how much ammonia koi excrete, but 1 gm of a typical koi food will produce around 40 mg of ammonia.  At the recommended feeding rate of 2% of the fish’s body weight per day, we would feed a one kilogram koi 20 gm of food each day. Simple arithmetic says that 20 gm of this food will produce a total of 800 mg of ammonia when it is metabolised.  This means that our average one kilogram koi on an average diet will excrete 33 mg of ammonia per hour.  It must be emphasised that this is not a precise amount, just a ball park figure to give an idea just how much ammonia the biological filter must process.

Most koi keepers are aware that in a biological filter, there are two species (types) of bacteria, that convert this ammonia, first to nitrite, which is also toxic, and then to nitrate which is relatively harmless to koi, except at high levels.  But do you know that these bugs need a total 7.2 mg of carbonate for every 1 mg of ammonia that they convert? Ignoring complex chemistry and thinking of this in simple terms, you could say that a healthy “diet” for the biofilter as a whole, is one part ammonia to seven parts carbonate (plus some oxygen of course, about four parts).  The bugs in a biofilter cannot convert ammonia without both carbonate and oxygen.  Koi also need a source of carbonate too, but to a far lesser extent. The easiest way to add essential minerals and trace elements is to use a reputable pond clay.

What is pond clay?
Not all clay is suitable for pond use, but there are two basic types of clay that are suitable:  Montmorillonite and bentonite.  Montmorillonite was named after the town near where this type of clay was first discovered; Montmorillon Clay Kusuriin France. Bentonite was also named after the place nearest to where this type of clay was discovered; Fort Benton which is near Montana in the USA. Montmorillonite is a very soft clay, rich in silica and other minerals.  It has a very fine particle size of about one micrometer (one thousandth of a millimeter in diameter).  Bentonite is a form of clay that is formed from volcanic ash and actually consists mainly of montmorillonite. There is no single chemical formula for these clays; the exact chemical make-up depends on the actual location where it is mined.  There are even small variations in the clay from a particular area as the mining operation digs through different layers of the deposits, which is why there is little hard data about what minerals any particular product contains.

If you read any of the websites that promote and sell clays, a common theme is that they contain anywhere from 16 to 78 essential minerals including calcium, magnesium, potassium, manganese, sodium or calcium carbonate, and iron.    In the Yasawagi district in the Japanese prefecture of Akito where clay is mined, it is known as “Magic White Soil”. This is because it is their “secret” remedy for many ailments including diarrhoea, toothache and just about every physical injury.

Is this medicinal use of any benefit to koi?
I can fully understand how “Magic White Soil” can work in the intestinal tract when taken as an oral medicine.  Clay particles are so small that they are physically tiny when compared to the size of some bacteria. When doses reach infected mucous membranes in the intestines, the clay particles completely envelop the bacteria. These are then cut off from their “food” supply by inorganic material and, as such, can no longer absorb nutrients and multiply. I doubt that this will happen in a koi pond unless so much clay is added that it forms a thick layer on the pond floor so that insects, worms and larvae would be able to colonise this layer.  In this case, koi would rummage through it for food.  Any food they found would be coated in clay particles.  In this way they would ingest particles of clay in sufficient quantities to have an effect on bacteria in their intestines, but not otherwise.  In relation to koi health, possibly the greatest benefit comes from the minerals in pond clays.

....in the Japanese
prefecture of Akito
where clay is mined, it
is known as “Magic
White Soil”..........

Koi, like us, have an immune system.  Its job is to keep the fish as healthy as possible.  Many circumstances can weaken our immune system, or theirs. One circumstance that can be detrimental to an immune system is lack of essential vitamins, minerals and trace elements.  I eat a sensible diet in order to ensure that I do not run short of any of these.  Koi in a pond are in a slightly different situation.  Carp are omnivorous; they will eat whatever they can find.  In the wild they will find a whole range of food so they will be sure of obtaining everything they need to stay healthy.  In ponds, we do not allow a build up of detritus that could decompose and break down into its component minerals, so koi will not be able to find food that is buried in the mud at the bottom. Apart from the occasional insects or larvae that they may find in their pond, it is our job to supply everything that they need. Clearly we should feed them a good quality food and supplement this with treats such as the usual prawns, oranges, lettuce etc. But in the wild, they would also be able to absorb dissolved minerals direct from the water.  These minerals are absorbed through the gill, the gut and to a small extent, through the skin itself. In a pond, they can only absorb minerals that are either already in the mains water supply or which are artificially added, for example in the form of pond clay.

What if we don’t add essential minerals?
There is a difference between water in which koi can survive, and water in which they will thrive. A question we should ask ourselves is;  “If I was given a fish that had just won first prize in a koi show, against good competition, would it still be a contender for first prize against similar competition at the next show, after keeping it in my pond for a year?” Many different factors would influence the situation but water quality will have a great effect on whether  the koi would still be in as good condition the following year.

What do clays do to the water?
In trials, some of the most well known clays were tested for their mineral content and their effects on water. The amounts of five major chemicals in these clays were tested.  The results showed considerable variation in levels.  (Click here for the results). Two of the samples showed negligible levels of manganese compared to the others but, interestingly, were considered to be among the top three for overall performance and price. All the clays were found to increase both pH and hardness. Some quite dramatically. Koi are tolerant of a wide range of pH and hardness provided the actual levels are stable and do not vary abruptly.  They are particularly sensitive to variations in pH of more than 0.2 per day.  I would strongly advise that if clay is used, the recommended dose rate is not exceeded.  While there is unlikely to be a large increase in pond pH, it should be remembered that ammonia becomes more toxic as the pH increases.  Do not add clay to a pond where there is an existing ammonia problem, it may make matters worse.  Curiously enough, the toxic effects of nitrite are exactly the opposite. Nitrite becomes less toxic as the pH increases, but do not take this fact as a recommendation to ignore a nitrite problem and simply mask it by adding clay to raise the pH. I am unashamedly fanatical about regular testing of koi pond water parameters and since tests for pH and KH are just as important as tests for ammonia and nitrite, this is yet another reason not to forget to test water parameters, especially when clay is used.

What benefits does clay bring?

There is a difference between water in which koi can survive and water in which they will thrive.......

Calcium bentonite clay, as the name suggests, is rich in calcium.  This mineral cannot be synthesised by fish, and apart from being vital for strong bones and scale development, it is a catalyst for enzyme action and other metabolic functions.  In addition to this, calcium bentonite has what chemists call “a negative electrical charge”. Molecules are not little magnets, but for those who may find the concept of molecules and their charges difficult to understand, they can be thought of as behaving just like little magnets. With magnets, like poles repel each other, but opposite magnetic poles attract each other and will stick together if they come close enough.  It is similar with molecular charges.  Like charges repel and opposite charges attract each other. A negatively charged molecule such as calcium will attract positively charged impurities to it.  Although these calcium molecules do not actually remove impurities from the pond water, nor do they make them vanish, they will be permanently locked together and, as such, they cannot affect the fish. Then, when the clay is filtered out as sediment in the filter bays and flushed away, it takes those pollutants with it.  In this way, toxins such as heavy metals, free radicals, and pesticides are removed from the pond.

What else will it do?
Being a very fine powder, and being heavier than water, clay acts as a flocculent. This means that as the individual grains of clay mix with the water then fall to the bottom of the pond, small floating particles are attracted to them and are pulled to the bottom with them, leaving the water clearer.

....In this way, toxins such as heavy metals, free radicals and pesticides are removed from the pond.....

The above discussion of clay is simple science (for some) and, as such, these points can easily be proved to be true rather than just being manufacturer’s hype.  There are, however, some claimed benefits that are much harder to prove without a full chemical analysis of what exactly is in the various clays that are on sale. Manufacturers are reluctant to give away their trade secrets and will not provide this information, but some of these claims are supported by anecdotal evidence.

Bentonite clay kills blanket weed. This may seem like a wild claim, but there are repeated stories to support this, including one user whose clay was accidentally knocked over and spilled into the pond.  This went unnoticed until the following day when all blanket weed around the area where the clay had settled had died.

Possibly the single most important reason why many koi keepers use clay is because it improves koi skin quality and adds gloss to their colours. Again, this is subjective and hard to prove but there are a great many koi keepers who say it does.  They can’t all be wrong.

The original idea for this article came from a forum thread about pond additives where the question was asked: “Does Sakai Hiroshima waste millions of yen a year on Refresh powder?” I think the answer is: “No he doesn’t”.


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