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Chris on Koi

Bursting Bubbles

The life functions of koi are similar to that of other animals in that they have muscles, skeletons, skins and internal organs which function in approximately similar ways. There is however, one great difference between fish and animals - fish live in water. More importantly to our circumstances, koi in ponds live in a limited volume of water.

A limited volume of water means that there is no continuous incoming freshwater source as would be found in a mountain stream for example. The only water available to our koi is what is in the pond.
This may sound like grade one logic, but we must keep this fact in mind - all the time. A koi's body is composed of about 80% water, much the same as ours. Therefore, koi are literally sacks of water separated from the pond water by a membrane (it's skin)! Thus to understand what water means to a koi is to lay the foundation for a more complete understanding of what a koi needs to survive. Any changes in the pond environment (water) will have an immediate affect on the koi. The greater and more sudden the change the less likely the koi will be able to adapt and the less likely it will survive. Transferring koi directly from one pond to another with a temperature change of more than 3 or 4ºC can cause thermal shock and even death.

Water keeping is the key to koi keeping
We, as koi keepers, must keep this in mind throughout our koi keeping careers. Every time there is a problem - check the environment (water) first. Maintaining good water quality will maintain good healthy koi. Let us become water keepers before we become koi keepers.

Turning our attention to the question that is often raised - what is the single most important thing in koi keeping (or should we say water keeping?) The size of the pond - a good relationship with your bank manager - oxygen levels - the genetics of the fish - the depth of the pond or perhaps the food?

The most important point in koi keeping
Although there are several contenders for first place however, the single most important factor in koi keeping has to be oxygen levels in the water. The second most important factor must be pure water. This is water free of the toxins ammonia, nitrite and nitrates. A host of other key factors run a close third, forth and fifth places to these two.

Why Oxygen as number one? This assumption is based on the fact that everything that lives in the pond environment is dependant on oxygen to survive. Without oxygen nothing would be alive, no fish, not bacteria (that we want) nothing. Anaerobic bacteria would flourish – but do we want that. If a koi is placed in a plastic bag completely full of water which is then sealed from the atmosphere, the fish will suffocate within a remarkably short time. The efficient gills will simply extract all the oxygen from the water and because it is cut off from the atmosphere vital oxygen cannot be replaced. We, therefore, have to consider this fact as the most important as it will affect the well being of our fish and pond system first.

The atmosphere has an abundance of oxygen. About 18 - 19% of the atmosphere is oxygen. This is around 250,000 ppm. The water in our ponds can only have about 8 - 10 ppm of oxygen and 14 ppm at saturation levels. The method of measurement as parts per million (ppm) is also often quoted as mg/litre i.e. milligrams per litre. Koi need at least 6 ppm to survive AND have reasonable growth. That's not much oxygen when you think about it. The saturation level of oxygen is dependant on atmospheric pressure (altitude) and temperature. The warmer the water the less oxygen it can carry.

Examine the following figures keeping in mind that at highveld altitudes (Johannesburg is 1800 meters above sea level) there is about 18 - 19% LESS oxygen in the water at any given temperature. The water temperatures can reach 25 - 30°C in summer in certain areas.

At sea level at 0ºC there is a saturation level of oxygen in water of 14.60 mg/L. In practice this is useless to koi. At this temperature the fish is probably close to death or would prefer to be dead if it had a choice. It is in a state of deep hibernation with virtually no active body functions. At 10ºC saturation levels of oxygen are around 11mg/L. A good healthy level, but again at this temperature the koi are not utilising much energy or producing much growth. Their oxygen requirements are therefore, limited.
At 20ºC oxygen saturation is down to about 8.6mg/L. This is exciting BUT not only are the koi more active at this temperature so is everything else. Algae adds oxygen to the water during daylight but removes it at night. The biofilter CONSUMES substantial amounts of oxygen while doing it's job. Any decomposing material such as leaves, dead algae, atmospheric borne pollution etc. consumes oxygen during the process of decomposition.

There is continual competition for a limited amount of oxygen in the pond
Further along the scale at 25ºC, saturation is down to 8mg/l. At 30ºC we are approaching oxygen levels that are critically low - 7.4mg/l at sea level, below 7mg/l on the highveld. Koi can survive at oxygen levels below 6mg/l. Their tolerance level is given in some reference material as a minimum of 3mg/l and in others as 4mg/l, but, growth will be restricted and colour will be poor simply because like all living creatures their bodies utilise oxygen to convert food into energy and growth.

As a further example of critical oxygen levels, if we have a measured oxygen level of 7mg/l in our ponds instead of 8mg/l this should never be viewed as only 1mg/l less than optimal. Having 7mg/l instead of 8mg/l is 12% less oxygen available in the water. The oxygen saturation figure at a given temperature is taken as 100%. Oxygen levels that are lower than optimum place the whole system at a disadvantage even before life in the pond starts competing for the limited oxygen supply.

Levels of oxygen in all types of ponds and dams are critical. It affects the growth, the colour and the health of koi.

Low oxygen levels increase the toxicity of ammonia. Continuous low levels of oxygen cause the fish to become lethargic and have poor appetite, and gills can be damaged resulting in bacteria infections. Low levels of oxygen in ponds will also adversely affect the bio-filters performance.

Unfortunately, oxygen levels in the water and temperature are not synonymous with each other. High temperatures affect the health of fish because the D.O. (dissolved oxygen) is LOWERED. While the B.O.D. (biological oxygen demand) of the whole system and fish is RAISED. Higher temperatures increase the toxicity of certain substances in the water and the invasiveness, and virulence of bacteria and parasitic pathogens. Up to a certain point higher temperatures produce faster growth but often with fading colours.

Oxygen in pond water

The top line represents the decreasing levels of oxygen as the temperature increases at sea level. The second line represents the oxygen levels on the highveld of South Africa (1400 meters or 6000 ft above sea level). The third (broken) line represents generally accepted minimum optimum levels of oxygen.
The optimal temperature for koi keeping is 22 - 28ºC. At this temperature there is maximum growth for a given amount of food ratio. However, above this temperature there is a fall in the conversion of food to energy and growth because of the relative fall in available oxygen levels.

We, therefore, have to explore ways of increasing the oxygen levels in our ponds.

Oxygen can only enter the water by diffusion between molecules of water in contact with the atmosphere. This leads to some interesting deductions. a. all the water's molecules should be brought into contact with the atmosphere at some time or the other (circulation) by drawing from the point furthermost away from the atmosphere (the bottom) b. the water should ideally be brought into contact with the atmosphere as much as possible (surface area and turnover rates) to assist with the diffusion of oxygen into the water and the release of unwanted gasses into the atmosphere.

In order to achieve this the pumping system must run 24 hours a day and your turnover rates must be as fast as possible
  • Algae - produces oxygen during the day but removes it at night. Studies have found that in ponds with relatively high stocking densities and blooms of plankton algae the algae removed more oxygen from the water than the fish during the course of the night. Turning the pump off at night will produce large rises and falls in oxygen levels. (Large, rapid variations of any kind in the pond environment are stressful to koi.)
  • Fish need oxygen to convert food into growth and energy. In warmer water this is happening all the time. Therefore, the oxygen levels have to be high all the time.
  • The biofilter consumes considerable amounts of oxygen converting ammonia to less toxic substances. The more mature the filter the greater the biomass needing oxygen.
  • Decomposing material consumes oxygen.
  • Ponds with low levels of oxygen have other problems. Low levels of oxygen result in higher carbon dioxide levels in the water. This in turn causes the koi to give off less carbon dioxide which in turn affects the pH in the micro environment of the gills. This area will become more alkaline (higher pH) and therefore, the ammonia that is excreted becomes more toxic in that immediate, sensitive area.

Calculate total running costs before buying a pump
When buying a pump look at the amps it draws. This should be given on the casing or the box. Then look at the volume of water it moves through unrestricted pipes. Check the volume of water at the head (height) you need water as the performance of some pumps drops off substantially the higher the water has to be pumped. Take the purchase price of the pump and add the monthly running costs over a period of say three years. This will give you the actual total costs of the pump over three years. Comparisons can then be made between different pumps and the budget you are working with.

Oxygenating the water via waterfalls or streams is a simple method that will add to the visual beauty of the pond and create pleasant sounds in the garden. Waterfalls should be designed to spread the water if possible, thus increasing the interface between the water and atmosphere. Design features and construction hints for waterfalls and streams will be discussed in depth in another Chris on Koi story.

When confronted with options regarding flow rates through filters and over water falls, always take the option for higher flow rates rather than lower flow rates.

Higher flow rates will bring more water into contact with the atmosphere at a faster rate and therefore, there will be more dissolved oxygen in the whole system. This is the fundamental of making the water become "alive". With higher flow rates any water that is considered "too much" for a biofilter can be diverted over a water fall or back to the pond to create circulation. Venturies can be attached to the returns. There are an infinite number of ways of utilising high flow rates but there is nothing that can be done about slow flow rates.

Circulation in a pond is considered essential. Circulation from the bottom to the highest point (waterfall or return to the pond) is the fundamental step in water keeping. Circulation around a pond is also a good idea as this distributes oxygen and impurities evenly in the water. It also avoids "dead" areas that sometimes occur in ponds.

One last thought on oxygen. Stocking densities affect the oxygen levels in water. More koi = more oxygen consumed. Never over stock a pond, especially one with a small surface area that is deep. Why? Because in the event of a power failure there is a small interface between the water and the atmosphere - the fish will suffocate after a time. The higher the stocking densities the quicker this will happen. This can be a very real problem at night or when you are away from the home and there is a power failure. The larger the fish and the greater the number in a pond the more chance of this happening. It is a very real problem.

Other factors affecting oxygen levels
Temperature is the most obvious factor affecting oxygen levels but there are other factors. The most common one pertinent to koi keeping is salinity (salt). The higher the salinity levels in pond water the less oxygen the water can hold.

Can we have too much oxygen in water? The answer is yes, but only under certain conditions. The pond can become super-saturated with oxygen. Ponds with massive algal blooms and a full day's sunlight can become supersaturated with oxygen. Koi can die from super-saturation of pond water with oxygen.

Ponds that become supersaturated have little or no circulation and unacceptable algal blooms. Super saturation of oxygen by venturies is not common. Although venturies work under pressure, oxygen is not the only gas in the atmosphere. Nitrogen is more abundant in the atmosphere and more easily dissolved in water than oxygen. Therefore,  if a venturi is placed in the pond it should not be deeper than about 30cm below the surface. The reasons for this is to prevent nitrogen entering the pond water under pressure and koi swimming into the bubbles. The area immediately around the venturi will have a different pressure gradient than the pond and 'gas bubble' disease could result when the koi swims from one pressure region to another. This is much the same as the bends that deep sea divers suffer from when returning to the surface too quickly.

Chris Neaves

Last Updated on Friday, 31 October 2008 14:23