How to Build a Koi Pond

How to Build a Koi Pond

Many people enjoy the hobby of keeping fish often in small domestic aquaria and even more people have a love of gardening with a water feature being high on many wish-lists. It is hardly surprising therefore that the outdoor Koi pond has now become so popular. Although the idea of a water garden may have had oriental origins, people all over the world have come to appreciate the sense of tranquil calm that such an environment promotes together with a feeling of connection with nature especially when watching the mesmerising activities of swimming Koi Carp which have been described as “swimming jewels”.

To the casual observer this all seems so natural and creating a Koi pond may seem to involve nothing more than digging a hole, filling it with water and adding fish but successfully keeping koi involves so much more and anyone contemplating building a Koi pond should carefully plan the whole operation as trying to rectify mistakes later can turn out to be much more expensive than getting it right in the first place.

Types of Pond Construction

The first consideration is the location of the pond and although aesthetics may be of less importance to a commercial fish breeder than a gardener, most people will be looking for a structure that is an attractive feature blending in with its surroundings but the physical features of the site also need to be fully assessed including the location of underground services such as drains and water pipes or the proximity to trees which not only shed leaves into the pond but their root systems could potentially cause damage to the pond structure. Having selected a suitable site, it is then necessary to determine whether the pond is to be of the traditional fully excavated type, completely above ground or, semi-submerged. Each type has its advantages and disadvantages but the fully excavated type is probably the most widely preferred.

There are various different ways to build a pond ranging from the traditional landscape gardeners’ method of clay lining to the installation of a small preformed plastic or glass fibre garden pond but the Koi pond will almost certainly be built either of a brick and concrete construction with the inner surface rendered watertight by means of a special coating or simply by employing a watertight pond liner in an excavated pond.

Pond Design

All design considerations must centre on the welfare of the fish and in this case size really does matter. A larger pond results in a much more stable environment in terms of water quality and temperature. Although there are no hard and fast rules, a water volume of less than about 4,000 litres is unlikely to prove adequate. The actual shape of the pond is a matter of personal choice but a large surface area gives improved natural gas exchanges whereas a greater depth provides for better temperature stability so many ponds are constructed with graduated depths with shallow margins possibly 2-3 feet deep and deep areas going down to maybe 6 feet. Such a design allows for the planting of Koi-suitable plants at the pond edges.

Practical Considerations

Although a pond may seem to be a very simple structure, it needs to extremely strong. Even the smallest of above-ground Koi ponds will hold water weighing around 4 tonnes and so adequate ground preparation is essential. The base of such a pond will normally be specified as being formed from a 6 inch layer of reinforced concrete but many pond designers specify the use of plastic fibre reinforcement in preference to the more traditional steel. For excavated ponds utilising liners, the main consideration is the maintenance of the integrity of the liner. The excavation must be completely free from any sharp stones, tree roots etc. and the bottom surface is usually covered with a layer of soft sand. Old carpets or thick layers of paper or cardboard are sometimes used. Another important problem when using liners is that when the pond is filled for the first time, the liner will mould itself to any irregularities and will tend to pull its overlapped edges inwards so it is essential to always allow a very generous overlap and never trim away the excess until after the pond has been filled.

Pond Equipment and Plumbing

For those looking to create a truly natural looking pond, there is a temptation to hide away all of the necessary hardware but this may be a mistake as good access is required to every part of the system. The pond equipment is designed to maintain optimal conditions for the fish and those who have previously kept fish in a small tank will already be familiar with the general principles but for the pond everything is on a much bigger scale. Putting it simply, Koi produce waste and lots of it. The first requirement therefore is an effective filtration system. The favoured location is to draw out contaminated water from a bottom drain located at the lowest part of the pond. Large ponds may need more than one such outlet. The advantage of using a bottom drain is that waste is effectively gravity-fed and is removed with the minimum of disturbance. It then typically passes through a mechanical filtration system to remove solid particles. Various different types are available but one of the most popular employs a vortex system which works on a similar principal to cyclonic vacuum cleaners. The water then passes through to a biological filter where it is purified by the action of bacteria. The growth of algae is always a potential problem in ponds and its presence is often associated with a healthy balance of nutrients but no one wants their pond to be covered in green slime and so an ultra-violet light source is usually incorporated within the water treatment plant. Some equipment simply clarifies the water while others actually have a sterilising effect. The usual way in which UV treatment works is that it causes the algae to flocculate i.e. to clump together allowing it to be removed by the filtration system. Skimmers are used to remove surface contaminants and oxygenation is usually provided by means of air pumps and air stones usually discharging at the deepest parts of the pond. In the UK heating is not normally required and Koi are considered to be cold water fish but some fish breeders may prefer to incorporate water heating to maintain a steady temperature at all times.

Pond Maintenance

All pond maintenance is aimed at keeping things right for the fish and the pond owner will need to have suitable test kits for checking on the levels of ammonia, nitrates, nitrides and pH. Even with the best water treatment equipment, some levels of contaminants will increase and so it is essential to provide adequate water changes. The need for these changes varies according to several factors but, as a general rule, about 10% of the water should be replaced each week to keep conditions as stable as possible.

So the peaceful swimming of these exotic fish may represent the very essence of tranquility but is only possible because of the hard work and dedication of the pond builder. Some ponds become a haven for wildlife with the Koi playing their part in insect control and features such as waterfalls can be both beautiful and helpful in oxygenating the water. With just a little forethought and careful design, a Koi pond can become a truly magical thing. Every garden should have one.

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