Alan’s Book

Chapter 1 Pond Design & Planning

A koi pond will be a permanent feature in your garden so it would be wise to get it right the first time rather than have to add certain features later. Take time to consider the following factors some of which may apply to your particular circumstances, especially those which relate to your water supply.

Be aware that a pond system should be designed to accommodate the water that is available for you to work with and create a suitable environment for the koi or other fish which will live there.

To successfully keep koi or any other pond or aquarium fish, you need to understand how to keep the water in a suitable condition for them. If you provide suitable conditions for your fish they will usually look after themselves; generally speaking you look after the water and the fish will look after themselves!

Before commencing with a pond build certain factors should be taken into consideration such as the suitability of the ground, the position in the garden which may affect viewing from the house as well as access to the pond on cold winter days. The provision of a pergola with a roof is most desirable and important for shading and to prevent the ingress of rain; the provision of services such as electricity and water are essential; access to a drain is also preferable. Koi are not cold water fish so some form of heating should be considered. Options are to heat using electricity or via a central heating extension from the house or even a dedicated boiler. Long runs of central heating pipes would require good insulation so this option works best when the pond is situated close to the house or housed in a structure adjacent to the pond.

A koi pond will require a biological filter; the success or otherwise of any koi keeping experience will largely depend on the filtration system employed and it is preferable that this be sited as close to the pond as possible in order that pipe runs to the pond, and the water from the pond to the filter system are kept as short as possible

Tap water is supplied for drinking purposes, not koi keeping! In some areas and in most areas most of the time, sterilizing agents such as chlorine or chloramine is added to the supply water to ensure low levels of bacteria in drinking water.

Occasionally higher levels of steralising agents are added after work on the distribution system. This can happen when the supply lines have been disturbed due to maintenance work or because the water source has been changed for some reason. Due to this it is wise to include a purifier/filter which continually prevents chlorine from entering the pond system into to water supply to the pond. If high levels of chlorine are allowed into the system it can sterilise the filter chamber and stop the beneficial bacteria from processing the toxic ammonia which is produced continually by the koi. If this happens ammonia can build up to toxic levels in the pond system to the extreme discomfort/stress of the koi.

Some water supplies contain levels of heavy metals such as copper, lead, zinc and aluminium. It is always good practice to have the water supplies checked for these metals and if they are found to be higher than the recommended safe levels for koi keeping, suitable in line purifier/filters should also be installed into the water supply which feeds the pond.

At this early stage of it would be wise to ascertain whether the water supply for the pond project is soft or hard. If you are cursed with soft water it would be wise to include a chamber in the filtration system into which materials can be placed in the water flow which will increase the hardness and alkalinity of the pond water. If your supply water contains significant levels of nitrate and phosphate levels it would be advisable to incorporate some means of controlling these and the effects which they may cause. (More later)

Any pond being constructed with sensible planning will incorporate filtration which is “gravity fed” from bottom drains in the pond. A gravity fed system is one where water is pumped from the filters into the pond. The water level in the filters drops and the pond water level will rise.

Large (4″) pipes are connected from a bottom drain to the inlet side of the pond filter and the pond water flows through this pipe to the filter due to the difference in water levels. The large pipes allow a slow movement through them and any solid waste is carried to the filter system without being unduly broken up as would happen if a pump was used to transfer the water to the filter system.

Pond water gravity fed filters (biological filters) have their water levels the same as that of the pond and this should be catered for in the design stage of the pond. The end product of biological filtration in koi ponds is nitrate and nitrate levels can build up to undesirable levels in such ponds. An ideal filtration system would incorporate means of reducing nitrate levels and this can be accomplished in a variety of ways as explained in chapter eight.

Where possible the pergola should cover the whole pond and extend sufficiently beyond the pond boundaries such that viewing can be done even if it is raining. If the pergola is planned at the outset it can vastly improve the working conditions for the building work in providing shelter from rain. It will allow brickwork and other jobs to proceed regardless of the weather.

If the filter system can be located close to the pond, the same pergola structure could cover the filter too and provide shelter in inclement weather when filter maintenance is performed.

Above/partially above or “in ground” pond?

A pond depth of five feet should be considered the minimum depth for a koi pond; this depth will allow stable conditions even in cold winters. A decision needs to be made as to whether the pond will be raised above ground level to say two feet, and be dug out to allow a further depth of three feet. Land conditions may influence the decision as sometimes rock or other factors prevent digging any deeper than three feet.

Suitable access for a mechanical digger may also influence the decision on the depth of your pond and the disposal of the soil and clay from the excavation needs to be taken into consideration. In large gardens the spoil from the excavation can sometimes be distributed around the garden by forming raised bed areas and rockeries but generally speaking it will need to be removed from the site, typically using skips.

If it is decided to make the pond six feet deep, the above ground dimension is best kept to a maximum of two feet as this height is ideal for viewing the koi whilst sitting close to the pond. If it is necessary to build the pond five feet above ground, raised decking or some such means of reducing the height to two feet from the ground level to the coping stone surround of the pond will improve viewing conditions.

Generally speaking a raised pond fits in well with a formal patio surround, whereas the “in ground” pond looks better with natural garden/rock surroundings. An “in ground” pond should always incorporate some means of preventing ground water from entering the pond.

Because koi ponds utilise biological filtration, another very important consideration is the shape of the pond. The shape and direction of flow in the pond will influence the way in which solids are removed from the pond. Solids removal (removal of waste matter) is one of the most important considerations in koi pond design!

The perfect pond shape for solids removal is a circle which incorporates a bottom drain at its centre. Removal of solids from the pond floor into an area where it can be discharged regularly is one of the most important issues in pond planning.

A square pond may be considered as circular with respect to water flow by rounding off the internal corners as shown in sketch 2

In formal landscape situations circular ponds look well and work well however it is possible to vary the pond shape to suit the setting as long as certain principals are followed.

The sketch shows a pond with one bottom drain located at the centre. The 1 metre area at either end should clear of detritus especially if the internal corners of the pond are rounded as shown.

If the length of the pond is increased to 6 metres it would be advisable to incorporate two bottom drains as shown above.

Ponds with various ratios of length and width can be arranged to work satisfactorily by the positioning of further drains keeping the same principle of the circle diameter being the most effective distance from the drain for waste removal. When designing your pond it is a good idea to draw a plan which is to scale and use a compass to describe the effective clearing distances on your plan.

To maximise the benefits of the natural laws of physics, koi ponds in the northern hemisphere should have the pond returns arranged such that they circulate the water in a clockwise direction and anticlockwise in the southern hemisphere. This is because water will swirl in these directions as it enters the bottom drain. Watch the bathwater when you pull the plug and see!

The size of a pond will naturally influence the quantity of water it will hold; one cubic meter contains 1000 litres of water or one tonne (220 imperial gallons).

Filtration systems are often rated by the number of gallons they can process; this can be a confusing way to rate a filter! What it generally indicates is the quantity of water it can accept flowing though it. For example a filter which is rated at 2200 gallon generally indicates that it will allow between one third and one half of that quantity to flow through it each hour. It is essential that pond water passes though the filter system at least once every three hours. A preferable rate would be once every 2-2.5 hours.

If we take the pond example above with internal dimensions of 3 metres X 6 metres with a depth of 1.525 metres this would contain 27.45 cubic meters of water or 6039 gallons. In practice the pond would only be filled to within 100 mm from the top so it would be marginally less at 5640 gallons.

A single filter which can accept a flow rate of between (5640/3) 1880 gallons per hour and (5640/2) 2820 gallons per hour through it or two separate filters each fed by one of the bottom drains which can deal with between 940 to 1410 gallons per hour, would be needed.

A single filter would work from two bottom drains suitably arranged such that each drain has equal amounts of water flowing though it. This could be achieved by using a “T” piece and ensuring that each drain is connected to the “T” with equal lengths of pipe. Water will tend to take the easiest route and the shortest pipe will offer the easiest route!

Circulating pumps do not always produce the circulation of water which corresponds to their rating. Any obstructions such as ultraviolet clarifiers and in line heaters will provide a resistance to the flow and reduce it accordingly. The length of pipe runs and the number of bends incorporated into them as well as bio fouling which occurs when the system contains koi will also have a very significant affect upon the actual flow rates achieved; the use of 2” pipework and fittings will minimise this reduction in flow.

The pond you will be designing will hold many more fish per gallon and per square metre of surface area than natural ponds. The surface area of the pond plays an important part by acting as the “lung” allowing atmospheric oxygen into the water and allowing gases such as carbon dioxide and nitrogen to leave the pond water. Because the stocking levels are highly likely to exceed natural levels it is wise to ensure that all of the water in the pond is exposed to the atmosphere via the pond surface. This is easily done using bottom drains which have aerated domes. Suitable air lines of approximately 12 mm inner diameter should be installed during the pond construction which can be attached to the aerated drain covers from within the drain body. An air pump is used to inflate the domes and the rising air encourages the water at the bottom of the pond to rise to the surface continuously exposing it to the atmosphere where gas exchange takes place. This ensures that all of the pond water is oxygenated as opposed to only the surface layer.

From time to time certain “in pond” treatments may be required which will leave quantities of scum at the water surface. It is common for dust to accumulate on windy days and an oily film from oil leeched from pellets is not uncommon. Skimmers which return the surface water/dust/scum are often used to remove these substances from the pond surface but they usually end up back in circulation especially if the skimmer returns the water to the filter system. Inevitably the skimmed materials reappear as scum or DOCs on the water surface. Because of this I prefer to use an overflow or skimmer which discharges directly to waste; this operation may be continual or the overflow/skimmer can be used as and when required. Generally speaking scum is not processed by the filter system and is best removed from the pond system by discharging it to waste.

Ultraviolet clarifier (U/Vs)

A pergola will provide some shading protection from direct sunlight but shading alone will not necessarily prevent unwanted algal blooms from occurring which can turn the water green and interfere with the viewing of the koi, so it is wise to include an ultraviolet clarifier into the pond return pipework. These units are rated by wattage and are available in a variety of sizes. A 55 Watt unit should cope with ponds up to 4500 gallons provided some shade is provide by a pergola. As a rule of thumb 10 watt per 1000 imperial gallons should be used when sizing U/Vs.

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