Alan’s Book

Chapter 10 Managing your pond water

In managing our pond water the aim is to keep all of the parameters within safe limits and relatively stable. Little and often is the best approach!

The most important management procedure is the removal of solid waste which has been settled out in the first stage of the filtration system.

All koi deposit their waste products into to water in which they live and this immediately pollutes the environment!! Essential bacterial action will be necessary to reduce these toxic pollutants to less toxic substances.

Water in koi ponds is in a continual state of decline; typically the alkalinity reserves are used up and pheromone levels, dissolved organic waste and nitrates increase. It follows that more koi in a pond will produce more pollution and this will soon be noticeable unless the pond volume is large. Ideally some means of reducing the levels of dissolved organic waste, nitrates and pheromones will help.

No koi pond can ever become “permanently balanced” without refreshing water changes or some other means of providing the alkalinity which is continually being eroded by the pond processes. Dissolved organic waste, nitrates and pheromones can be diluted by water changes or reduced by other means.

Oxygen levels

It is unlikely that a properly designed koi pond with bottom drains with aeration will suffer from low oxygen levels. Koi carp require a minimum oxygen concentration of 6 mg/l in their environment; high temperatures, high stocking levels and high organic content will all tend to reduce the oxygen levels in a pond.

The oxygen budget

Temperature controls the amount of oxygen that a sample of water contains

All ponds have what is known as BOD. The biochemical oxygen demand of a pond is the background demand for oxygen by all the natural processes which are occurring such as bacterial action in the filters in reducing ammonia through the nitrogen cycle and the breakdown of organic waste such as fish faeces and dead algae

The oxygen levels in a koi pond will depend on the balance between the available oxygen and the consumption by background processes (BOD). The amount of oxygen which water can contain reduces as temperatures increase, but the metabolism of the pond increases within the normal range of pond temperature and as a consequence of the increased metabolism the general requirement for oxygen also increases. The koi also require more oxygen at higher temperatures within their normal range and will consume more food and produce more ammonia!

Keeping the pond clean and discharging the organic waste regularly will minimize the oxygen required to process this waste thereby lowering the BOD and increase the oxygen available for the essential bacteria and koi. Aerated bottom drains ensure that the whole body of pond water is exposed to the atmosphere where oxygen is absorbed through its surface.

Algal growth and especially blanketweed will introduce large amounts of oxygen during daylight hours but will consume large amounts of oxygen during the hours of darkness.

Maintaining the pH of the pond water.

Water changes made from water that is high in alkalinity can maintain the alkalinity of a pond at suitable levels; however koi keepers in soft water areas will need to buffer their pond water by adding calcium carbonate/bicarbonate to it, simulating what happens to rain water, which falls on limestone areas. Oyster shell and calcified seaweed (lithaqua) are good examples of such buffers and sufficient large quantities of such buffers should added to the pond system where the supply water is soft. Sodium bicarbonate will provide an instant supply of alkalinity and may be required as a regular addition to the pond water.

Providing supplies of calcium/magnesium carbonate are available in the pond system, the following reactions will take place:

CaCO3 + H2CO3 = Ca (HCO3)2 or K.H!

Calcium Carbonate + carbonic acid = calcium bicarbonate

(The CO2 is provided by fish and bacteria respiration; when dissolved into the water it forms carbonic acid. The reactions will take place more readily when the water becomes acidic (below 7 pH) offering good protection against a pH crash.)

The bicarbonates increase the alkalinity (K.H.). A similar equation occurs for magnesium.

Soft water, because it has little alkalinity can allow quite large upward changes in pH during daylight hours and downward changes during the night. This is not an ideal environment for koi although they can adapt to pH swings it is preferable that a stable environment is provided where ever possible. Increasing the alkalinity will help to prevent large swings in pH.

The GH or General Hardness test measures the soluble calcium, and magnesium ions in the water. Calcium and Magnesium are needed for koi coloration and health, since the required content of calcium in fish blood matches the calcium content of pond water when the water measures 250 ppm GH level.

Both calcium and magnesium are needed for bone and scale formation, meaning they are essential to koi coloration. The recommended GH for koi keeping is a range of 100-200 ppm. Values below 60 ppm sometimes lead to koi coloration loss, and values below 40 ppm usually lead to increased coloration loss, which is highly dependent on the availability of calcium and magnesium in the diet of the koi.

Having a reasonable amount of dissolved calcium in the water also helps prevent high pH in pond water by precipitating calcium carbonate to lower pH anytime the pH value drifts above a value of 8.5.

For those with a water source in the 80 to 200 ppm GH range, the recommendation is to “do nothing” since the source water has hardness in the correct range. For those with no measurable GH in the source water, adding equal amounts of calcium chloride and Epsom salts (magnesium sulphate heptahydrate) to achieve the recommended range of GH is suggested. 0.45 Kg of calcium chloride per 5000 lts (1000) gallons increases GH by 120 ppm, and, likewise, 0.45 Kg of Epsom salt per 5000 lts increases GH by 50 ppm.

Calcium chloride is sold in swimming pool supply houses for increasing water hardness. Both substances are relatively inexpensive and once the desired levels are attained in the pond system only small additions are required to compensate for water changes which are low in these substances.

As calcium and magnesium usually occur in ratios from 3:1 to 10:1 it may be advisable to use the 3:1 ration when adding these substances to the pond water.

To increase the GH in the 3:1 ratio and raise the G.H. from 50 ppm to 150 ppm, add 0.42 Kg of calcium chloride and 0.34 Kg of Epsom salts per 5000 lts (1000 imperial gallons).

Many source water supplies have significant phosphate content, with significant meaning 2 to 30 ppm values. Water Companies can add various phosphate compounds to the water either to control mussel growth in the water plant system, or to prevent pipe corrosion. Phosphate levels as above do not hurt the koi, but do make algae control very difficult.

To prevent algae blooms (green water) while using high phosphate source water, it is important to keep water exchanges small to avoid large phosphate doses to the pond, and enough desirable plant life to consume the phosphate levels. Keeping nitrate levels very low helps to prevent algae blooms from high phosphate. For those ponders with high phosphate in the source water, higher than normal wattage UV lights may be required to prevent green water algae blooms. One cautionary note on phosphate control is that phosphate is a requirement for growing biofiltration bacteria for ammonia conversion, so if the phosphate level is so low a really good test kit can’t measure it, and you are having biofiltration efficiency issues, it is possible you may have to actually add trace amounts of phosphate. Koi keepers who experience severe algae problems or poor biofiltration performance should consider buying a phosphate test kit.

Phosphate levels above 5 ppm can give uncontrollable algae blooms, while non-detectable phosphate levels can be the cause for poor biofiltration performance.

String algae, commonly called “blanket weed” will respond to high nitrate and phosphate levels in the pond water. There are numerous “cures” for blanketweed available on the market some of which work in some ponds but are completely ineffective in others.

The above notes on algae control apply to blanketweed as well as single celled algae which is the cause of “green water”. Algae are plants and need sunlight as an energy source to grow; shading the pond with a pergola in the absence of natural plants such as water lilies, which can cover and provide shade to large areas of natural ponds, will go some way to controlling both types of algae mentioned.

Water Changes

As our tap water has originated from rainwater some koi keepers may believe for reasons of economy and convenience that rainwater should be used to top up the pond water or be used for water exchanges.

It is essential that this practice is avoided!

As explained earlier rainwater may begin as “pure” water (H2O) but being a universal solvent it quickly absorbs gases such as carbon dioxide, sulphur dioxide and other contaminants which are undesirable to pond water.

Acid rain is a very real phenomenon and will quickly drive down the pH of pond water to dangerous levels. It does not contain the essential minerals required to sustain aquatic life nor does it provide any minerals associated with buffering the water (alkalinity).

Wherever possible rainwater should be prevented from entering the koi pond and the provision of a pergola with a solid roof will help to ensure this.

It is fair to say that, try as we may, we will never match the balanced system of a natural pond in our koi ponds: as stated earlier many processes occur in a natural pond which we can never replicate.

No matter how hard we try to avoid it, the water in our ponds will deteriorate; the rate at which this happens is directly related to our filter design, the amount of fish, and the amount and type of food we feed.

Changing water is believed to be the best solution to this water deterioration. In changing water we can dilute some of the undesirable dissolved substances to tolerable levels, and we can replace some of the essential minerals that the pond process uses too.

Chlorine in fish ponds

Chlorine at 0.2 ppm has higher oxidation potential than PP at 4 ppm and the chlorine is more likely to kill fish.

In changing water we must be aware that tap water will contain some amount of chlorine. Be aware that chlorine is very dangerous to the koi and the filters and levels of 0.2 ppm have a higher oxidation potential than potassium permanganate at a dose rate of 4 ppm!

If you are performing large water changes and the recommended flow rate through your chlorine filter is exceeded, you may be introducing high levels of chlorine to your pond to the detriment of the koi and the filter system! A wise precaution would be to keep a check on the chlorine levels in your tap water before water changes are made.

How Much must we change and how?

When we change water we can change the pond environment in several ways.

One of the keys to successful koi keeping is to provide a stable environment for them: in doing this, we provide a stable environment for all the other mostly unseen inhabitants of the pond too.

One of the most obvious ways we can alter the pond water during water changes is by temperature change.

If we emptied out half of our pond water and re-filled it, we would be making a substantial reduction in the unwanted portions of the water, but as supply water is often of a lower temperature than the pond, we could also reduce the pond temperature too.

Water has a high specific heat, which means it is able to resist fast changes in temperature. Fish living in water are not used to and therefore un-adapted to situations where the water temperature alters rapidly. So a basic rule in water changing is that we do it in a way that minimizes the temperature difference in the pond water.

Ponds come in many sizes so if we are to adapt a rule of thumb, it should be based upon what percentage of water change we do, as opposed to how many gallons we change. Another point to consider is, if we have a pond, which is heated, and we perform a water change from unheated water, this could cause a bigger temperature change to that water than that changed in an unheated pond.

Common sense must apply here. Usually an overall change of twenty percent per week would be acceptable. This could be achieved by daily solid waste removal combined with a constant trickle of water flowing through the pond and overflowing to waste. This is a useful way of removing the dust and other debris, which forms a film on the pond surface and can, inhibit the gas exchange referred to earlier.

It is best to add fresh water to the pond directly to the pond or into the last filtration stage where it is pumped directly to the pond. This will reduce temperature fluctuations as the new water is mixed with the larger water volume of the whole pond. When the mixed water enters the filtration system it will do so at a relatively stable temperature and any undesirable components of the new water will be suitably diluted. Adding new water into the relatively smaller volume of the filter system could cause undesirable wider temperature fluctuations to the filter beds.

Water changes will usually refresh the water and dilute many of the substances dissolved in it however substances such as pheromones and hormones which are excreted by the koi are used as chemical signals for such things as breeding readiness and a signal of population density. The signals which flag up population density are believed to retard growth to prevent the natural environment becoming overloaded.

The use of potassium permanganate is controversial and many koi keepers frown on the use of this oxidizing agent. It can be a very useful chemical providing it is used correctly and a very dangerous one when it is not used correctly.

When a good supply of water is available, water changes would be the preferred method of refreshing pond water however many keepers do not have good or plentiful water supplies and for those in such a situation the use of potassium permanganate can offer a solution to maintaining pond water in good condition.

Potassium permanganate (PP) can provide benefits such as the reduction of dissolved organic compounds (DOCs) and the destruction of hormones and pheromones, neither of which can be removed by the biological filter.

Dr. Roddy M. Conrad, who is a koi hobbyist of some renown and also a biochemist, has kindly let me use information with respect to his experiences using PP. He has mentored me though some of the water chemistry explanations and I duly thank him for his help.

Potassium permanganate used at the rate of 0.5 grams/tonne of pond water weekly or every other week is a convenient and safe means of reducing undesirable dissolved organic compounds and pheromones in koi ponds.

At this dose level t is unlikely that the water will remain purple or pink for any length of time the first time this water treatment is used. Once the water does remain purple/pink for 30 minutes after the addition of potassium permanganate, the water may be considered to be in decent condition and the dose rate may be lowered such that a 30 minute only correct colouration is achieved. Water which is low in dissolved organics can stay pink for periods of more than 30 minutes so doses of 0.25 grams per 1000 lts may be all that is required to maintain decent water quality.

In ponds with high dissolved organic content the water may go from pink to tea coloured in less than 15 minutes. If this happens treat again at the 0.5 dose rate for a maximum of 5 treatments.

If a calibrated ORP meter is available during these treatments the preferred ORP readings during low level PP treatment is in the 400 to 475 range (not to exceed 500).

It is normal to see a brown scum at the water surface after this treatment and this can be overflowed to waste via an overflow; in doing this the oxidized undesirable components of the pond water are removed completely from the system.

At the onset of this particular treatment the water will tend to be slightly discoloured but it should soon clear and you will notice a decided improvement in the water clarity.

Conservative Advice about PP use.

• Measure the volume of the pond so you know the PP dose you are using.

• If you have a good gram scale, use it to dose PP.

• If you don’t have a good gram scale, assume each teaspoon of PP powder is 8 grams.

• Don’t get PP on your skin unless you want brown stained skin. The brown stain will “usually” wash off with a hydrogen peroxide scrub if the skin stain is fresh.

• Don’t get PP powder in your eyes; it can cause blindness!

Nitrate levels

The end product form our biological filters is nitrate; ammonia (NH3/NH4) is reduced to nitrite (NO2) and then to nitrate (NO3).

High levels of nitrate in pond water are undesirable and may well be one of the factors which predispose koi to bacterial infections. They will also encourage algae in the presence of suitable levels of phosphate in the water.

If your pond system includes a trickle tower with media such as lithaqua or oyster shell this will should reduce the nitrate levels in the pond water and maintain the alkalinity too.

Some source waters contain relatively high levels of nitrates such as 50 ppm; water changes using source waters such as these benefit from a nitrate filter in the pond water supply line.

For further information on nitrate please refer to Filtration Systems -chapter 8.

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