Alan’s Book


It is generally recognised that the best koi have been developed in Japan. The natural waters of Japan are inherently soft and because of this many koi keepers believe that “soft” water provides the best living conditions for koi carp.

The emphasis on soft water for koi keeping is, in my opinion, one of the main reasons, if not THE main reason for problems in koi ponds.

I have seen some superb examples of koi which have grown substantially during their summer periods in mud ponds in Japan with skin and colours that have a superb lustre. The skin and lustre of koi is influenced by their diet as well as the water in which they live; it is highly likely that the mud in these ponds contributes essential components to the diet which compensates for the low mineral content of the natural water. However many such ponds only house a handful of koi such that each koi enjoys many thousands of gallons as an environment; this ensures that any growth controlling substances excreted by the koi are well diluted.

These ponds are usually conditioned by the addition of lime when they are emptied, and have oyster shells included into them when they are refilled in order to counter the effects of naturally soft water and encourage the production of plankton which forms the basis of the natural food chain as well as providing an element of buffering into the water to counter the effects of acid rain and photosynthesis, and help to provide more stable water conditions such as pH. These mud ponds are not self sustaining with respect to food supplies which are supplemented on a daily basis.

Some claim that growth rate is higher in soft water but I am not convinced that this is so! The “grow faster” claim is in contradiction to nature, as soft waters are less productive (produce less natural foods) than hard water. I feel that the sheer volume of water available for each koi provides massive dilution of any growth retarding pheromones which are excreted by the koi into the water and this has a significant effect upon growth rates.

It is claimed by some that the skin of koi living in soft water has more lustre and has better definition but another factor to consider is that high class Japanese koi will look best when living in the same conditions that their ancestors have been selected from. The genetic makeup of the selected koi is limited to a gene pool which fares best in their native “soft” water but who can say that all koi will exhibit better skin quality when they are living in soft water? Koi selected for good skin qualities from parent stock living in hard water may well produce equally good skin quality; perhaps the koi now being domestically bred and reared in hard water will confirm this point?

I am not convinced that low water hardness alone dictates the quality of the skin and I feel it is more likely to be a function of the overall quality of the water, and diet rather than hardness alone.

Many koi keepers do not appreciate that the koi in Japan which are housed in soft water in the mud ponds, enjoy very low stocking densities; there is a very important link between soft water, or water which is low in dissolved minerals, and stocking levels.

In a filtered and re circulated koi pond, stocking levels are usually much higher than mud ponds; it follows that the ammonia levels will also be higher as they are not as diluted as they are in large bodies of water such as large ponds and lakes. Plants are rarely available to consume the ammonia, so the job of ammonia removal is left almost exclusively to ammonia reducing bacteria. This is the important difference between mud ponds or other natural bodies of water and re circulated and filtered koi ponds!

My early attempts at koi keeping were fraught with problems, the vast majority of which were related to the environment within the pond. In those days help and experience were in short supply, and it was heart breaking to feel so helpless and to see so many lovely koi suffer problems and eventually die.

I have been fortunate to have been able to build a few mud ponds which were stocked with indigenous fish and carp; these are self sustaining in their food chains and fish stocks. This has allowed me a better understanding of how we are contradicting Mother Nature by endeavouring to keep relatively high numbers of fish in low volumes of water in our ponds at home. At the same time it has made me aware of the shortcomings of our “unnatural” ponds and this awareness has drawn attention to the areas where we can compensate to some degree the un-naturalness of our own koi ponds for the benefit of the inhabitants.

The object of this book is to pass on useful information specifically gained by experience in keeping koi in filtered and re-circulated ponds. All water in filtered ponds requires careful management to provide better than survival conditions for our koi.

Soft water in filtered ponds requires more careful management, and is often the major cause of problems in koi keeping.

The following chapters which include pond design and construction will give some guidelines on how pond shape and water circulation can influence the ultimate quality of the water in the pond and improve the environment for our koi. They will also highlight the problems associated with soft water and offer some advice on how to deal with it.

Perfect water is not practically obtainable, however with an awareness of what perfect water should be, we may be able to achieve an environment for our koi which is way beyond that in which they can simply survive.

It is rather difficult to isolate individual topics into isolated chapters because many important topics such as ammonia, filtration and water quality overlap the individual chapters. Where it is necessary, important subjects are repeated when they are relevant to the particular chapter.

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