02. Providing Koi with the best pond conditions

Having established the environmental requirements for koi in step one of the 10 steps to successful koi keeping, step two naturally progresses on to how we provide our koi with those conditions. At every stage, it will also be helpful to clarify why each of the factors is so important for the well-being of our koi.

In step one, we quite surprisingly suggested that the best environment for our koi is a natural mud pond rather than a clear and filtered koi pond. Koi exhibit their best condition when reared in this natural environment as it supplies their every need in an unrivalled way. The mud pond is the ‘benchmark’ against which we can compare the conditions we provide for our koi in a traditional artificial koi pond. I would go as far to say that if we all kept our koi in the haven of a mud pond our koi would fare far better than when they’re kept in an artificial koi pond.

It is also far easier and less time-consuming to keep koi in a mud pond. There are no filters to clean or water changes to carry out and with the diverse ecosystem pandering to our koi’s every day needs our koi will show unparalleled condition. Quite simply, once stocked into a mud pond we can leave the rest to Mother Nature.

But because we want to see, and exhibit our koi in clear water conditions, keeping koi in a mud pond is immediately ruled out, and so too are some of the many wonderful benefits for our koi. As soon as we set out on this journey to successful koi keeping via the clear and filtered route, we cannot take the ‘passive’ clay pond approach but must consciously work harder at establishing and providing suitable conditions for our koi.

Mud Pond vs Filtered Pond – A Practical Illustration

The different conditions that koi experience when being kept in an artificial and a natural pond became very apparent when I used to farm koi for a living. In February, the broodstock were brought inside into heavily filtered and aerated artificial ponds, having spent the last seven months outside in a mud pond. From February to June the koi were matured in the best artificial environment under an artificial heat and light regime to accelerate the maturation of the eggs in the female brood fish. In mid-May they were stripped of their eggs and a few days later were returned back into their outdoor mud pond. However during the preceding months while being kept inside, these fine specimen working fish unavoidably got a little knocked or bruised (as can happen in any koi pond) and their condition and colour appeared to deteriorate even though they were in the best of artificial environments. Having spawned, and earned their keep for another season, these tired and slightly worn-out fish were returned to the mud pond in June where they were left alone until next February, barring a little supplementary artificial food. Upon harvesting the same fish the following February to repeat the spawning process, the broodfish displayed faultless colour, vitality and condition and were virtually unrecognisable from the slightly ragged and bruised specimens that were put into the pond back in June. The mud pond had provided them with many beneficial factors that were obviously missing from the vast recirculating maturation ponds, returning them to A1 condition, without any input from us. Leading koi keepers who are fortunate enough to be able to do so, put their finest specimens ‘out to pasture’ in similar mud ponds to enhance their condition just prior to a show. The mud pond performs wonders for koi health and condition, far in excess of what a filtered koi pond can achieve.

When considering what effects our environment can have on our own health, there is a similar comparison in our own lifestyles. Sick Building Syndrome is a phenomenon that causes health problems to those workers who are unfortunate enough to work in such a chronically stressful working environment, whereas a Health Spa set in the lush green rolling countryside is somewhere we may wish to spend a weekend to recover from the week’s work.

And so having decided on a clear and filtered route how can we ensure that our koi experience more of a Health Spa phenomenon in preference to a sick building syndrome?

Nature has set us targets, and we must try to get as close to those targets as is possible in a clean and filtered pond.

Regular testing. If you can measure it, you can manage it.

The only way to conclusively confirm that your water parameters (well the handful that we routinely measure, anyway) are on target to being true to a mud pond is to test for the parameters regularly. Our testing generally goes as far as investigating those parameters that are (or could be) potentially life-threatening with a few others detecting the ‘characteristics’ of the water. But if the truth be known, a mud pond is so much more supportive to koi because of a lot of other significant factors found in a mud pond that we would not routinely test for. It is these largely unquantifiable ‘X-factors’ that make our task of replicating a mud pond in a clear pond virtually impossible. Even if we could measure some of them, so alien is the artificial pond to the natural pond that it would not have the means to provide the missing factors anyway. Our unsolvable problem is that the beneficial water conditioning effects of such a diverse ecosystem that makes a mud pond ideal for koi, are largely unattainable in a filtered koi pond.

What achievable targets has a natural pond set us and how do we best achieve those targets in a filtered pond?

Biological water parameters. Every species of fish sets us a target of zero accumulation of toxic metabolic by-products such as ammonia (and its stable mate nitrite) although some species are more tolerant of these pollutants than others. The best way of ensuring our koi don’t experience ammonia or nitrite in a pond (as they would not in a mud pond, except perhaps a few days after spawning) is to stock it and feed the pond at a rate that your biological filter can manage. Assuming that the filter system is appropriate to the size and turnover of your pond (and recirculating water is another foreign experience for our koi) then the pond should be stocked gradually over months (if not seasons) to allow the numerous different types of bacteria to colonise the pond and filter system. This can be a difficult relationship to balance in the first few months of a new pond as the bacterial colonies will only grow and mature if they have the ammonia and nitrite to feed on, and yet at the same time, we want to keep ammonia and nitrite levels at zero. Regular testing in the early stages of a pond’s life will allow you to confirm that the stocking regime is appropriate to your filter’s capability. Furthermore, it is reassuring to see a slight blip in either ammonia or nitrite levels and to watch it disappear a day or so later. This shows that your filter’s ‘appetite’ for ammonia and nitrite is improving.

Less important to the well-being of koi are nitrate levels, yet for reasons of blanket weed and algae, these should be kept as low as possible in a filtered pond. In a mud pond, natural low-level production of algae would keep on top of nitrate levels, whereas in a filtered pond, we want to intervene and keep nitrates as low as possible ourselves in order to keep algae growth to a minimum. We are not interested in nurturing algae growth in a filtered pond as it is not vital in providing the foundation to our pond’s food chain – Our koi of fed on an artificial dry diet. I think most of us are guilty of taking our eye off nitrate levels, and if we do let them accumulate, we should not see levels in excess of 50 ppm, diluting excess nitrate away through regular partial water changes.

Chemical water parameters: These arguably are the factors that make the difference between the naturally supportive properties of a mud pond compared to the relatively barren environment of a filtered koi pond.

Before exploring some of the details we should confront an obvious paradox when comparing the two different pond environments. Having argued the many benefits that a natural pond has to offer over a koi pond, it is however more likely to show at greater degree of variation in water quality throughout the day compared to a filtered koi pond. This is particularly true for pH.

A mud pond is naturally a nutrient-rich environment that supports a continuous underlying amount of algae growth and other primary production. A green water pond will experience daily variations in pH as a result of the interactions caused during photosynthesis. In the daylight hours, the pond ecosystem is a net CO2 consumer, causing the pH to rise, whereas at night it becomes a net CO2 producer causing the pH to fall. In comparison, the pH of the filtered koi pond will be far more stable. The target that nature sets us is a pH between 7.0 and 9.0, with our objective for a koi pond being somewhere in between.

The pH is maintained in this alkaline band courtesy of the high mineral load of a mud pond, giving us a high GH and KH. GH is the measure of the hardness-forming calcium and magnesium salts, whereas KH describes the levels of soluble carbonates and bicarbonates that help to buffer the pH. We can enhance the mineral loading in our own ponds by using a combination of a source of calcium carbonate fitted in the filter and frequent additions of a high-grade clay. A mud pond is based on a clay substrate which continually releases minerals, continuously conditioning the water. As this is obviously not the case in a pond lined with an inert, man-made and impermeable barrier, we must regularly supplement the mineral load of our pond to try to close the gap.

Physical parameters. The physical targets set for us by a mud pond include its depth and turbidity. As we actively filter out all suspended matter to make our ponds as clear as possible we are largely concerned with satisfying the pond’s depth requirements. A deep pond not only provides koi with some stress-relieving security, it also helps to maintain a stable water temperature, particularly over winter. Koi are a warm water fish, but also require a period of cold weather in their seasonal calendar to reset their ‘biological clock’. An increasing number of hobbyists are heating their ponds over winter, in effect denying their koi of what nature has intended. Interestingly, there has also been an increase in the number of female koi becoming spawn-bound in heated ponds, having been denied the seasonal cues required for spawning. If you do insist on heating your pond over winter, take into account that your koi expect a cold snap and require one for the well-being of their physiology. By denying them a period of inactivity, you’re moving yet further away from the ideal conditions in which koi thrive in a natural mud pond.

Kill blanketweed and string algae.