Pond liner installation is one of five basic steps to creating your own Koi pond – the other four are planning, digging, installing the equipment and finally, adding your fish. The pond liner should be free of folds and creases to reduce the risk of uneaten food and fish faeces collecting and decomposing in them – which will eventually affect water quality and increase algae production.
Planning your pond
When you are looking for a site for your pond, start close to the house. There is little point in spending a lot of money on a pond full of beautiful fish if you have to trek up to the end of the garden to see them. Apart from missing out on the joy of Koi, there’s a strong chance that out of sight will mean out of mind. And a forgotten Koi is invariably found floating upside down.
Think about where the sun falls in your garden and don’t put the pond where it will be in full shade – especially during winter. Avoid trees as much as you can. Leaves will clog and pollute the water and roots could cause serious damage to the pond liner. Don’t forget, you will need to get an electrical supply to your pond, so think about cable runs and siting.
Then plan the size and shape of your pond. Remember, Koi ponds have to be deep, at least 1.5m and up to 2.0m – don’t go much deeper than that because at 3.0m sunlight can’t penetrate sufficiently to promote the vital growth of algae on the bottom. Also remember that Koi are big fish and need a large volume of water; they also produce large amounts of waste. For both those reasons, a steep or vertical sided pond is recommended. It guarantees the largest volume of water for the space occupied by the pond and steep sides don’t accumulate waste materials and debris that can release harmful ammonia.
Also, keep the design of your Koi pond simple. The simpler the shape – round, square, rectangular or L-shaped – the easier it is to maintain. A simple shape can always be disguised by creating border features with stones, rocks and plants – bear this in mind when purchasing your pond liner and underlay as both will need to extend beyond the limits of your border features.
Digging the hole
Unless your pond is going to be built above ground, you are going to be shifting a lot of soil even for a modestly sized pond – so consider hiring a mini digger – it will save a huge amount of time and effort (and blisters) – though may not give the same satisfaction. Before you start digging, mark out your pond using a rope or spray paint – even consider placing some rocks or plant containers around the periphery so that you get a better idea of what your pond will look like in that position. Make an allowance too for the block work which will form the inside walls of your pond and prevent groundwater leaching the soil behind your pond liner and causing potential damage.
If your pond is going to be longer than 2.5-3.0 meters, it is well worth while building a concrete collar around the outside of the perimeter- including any curves or features you have added to disguise the basic shape of the pond. The collar will not only prevent run-off from your garden entering the pond, but also provides a secure anchor for the pond liner. To create the collar, dig a trench about 10cms deep and 15-20cms wide and fill it with concrete to ensure it is precisely level all the way round. Now you can start digging in earnest, remembering to create any shallow shelves or ledges around the edge where feature stones and plants will be positioned. If you are going to create shallower areas for the fish, these should slope inwards. Bear in mind that the shallows around a pond are the ideal hunting ground not only for herons, but domestic cats too.
Once the pond is dug to the right size and depth, create the channels for the bottom drain, which will remove all the waste and the connecting pipe work (usually 110mm), as well as returning pipe work from the filtration system.
Once the base is levelled, and the bottom drain (or drains depending on the total size of the pond) is positioned, it can then be filled with 10-15cms thick of concrete. It is worth specifying a strong mix with plastic reinforcing fibres. The base should be sloping gently towards the bottom drain. Once the base has had a week or so to cure thoroughly, the block work for the walls of your pond can be laid. The wall should extend to the height of and ledge or shelf you have created around the pond. Again make allowances for any pipe work.
Installing the pond liner
When the walls are complete and the cement has been given time to cure, the protective underlay can be installed. The best underlays are very tough geotextiles made from mechanically bonded polypropylene. They not only protect the pond liner from physical damage, but are also gas permeable to allow any gases that build up underneath the pond liner to escape. This should be overlapped by 20-30cms and laid so that it covers the bottom and sides of the pond completely. At the top, it should extend across any shelf or ledge and over the top of the collar you have built around the pond. The underlay can be held in place with lengths of stout stainless steel wire shaped into large staples and pushed through the underlay into the soil around the edge at the top. It should be cut away closely around any bottom drains to allow the pond liner to be fitted to the drain. Once the underlay is in place, the pond liner can be fitted.
Because Koi ponds tend to be deep, steep sided and regularly shaped, consider ordering a box-welded pond liner in either Epalyn (EPDM) or Butyl made to the precise dimensions of your pond. It is worth waiting until your construction is complete so that you can measure the actual dimensions. A box-welded pond liner is much simpler to install and, if measured correctly, should provide a good smooth lining without wrinkles and folds which can trap waste matter. Again the pond liner should extend over any ledges or shelves and over the top of the collar, with sufficient extending beyond that to allow for soil or gravel to be laid on top to anchor it in place. Any areas of the pond liner which will be supporting plants, stones, or soil should now be protected with an additional layer of underlay.
Fitting the pond filtration system
Making sure that your Koi pond is properly equipped with the necessary water filtration and pond pump is critically important to the success of your venture. The ideal set-up will use a gravity feed from the bottom drain taking the water and waste to a filtration and cleaning process which will consist of a settling chamber, where the majority of the large solids are removed; a mechanical filter, which will strain even the smallest particles; and finally a biological filter where good bacteria are encouraged to consume chemicals such as nitrites and ammonia. In natural conditions there is sufficient water volume and surface area for bacteria to maintain a healthy balance in the water. But in an artificial pond, where the ratio of fish to water is much higher than in nature, you must provide additional space for good bacteria to do their work. If your pond is exposed to a lot of direct sunlight, you may also want to install an inline UV filter which will kill or damage the single-cell algae that cause green water during summer.
Once all your pond accessories are installed, it is time to fill the pond – and the perfect time to find out exactly how much water it will hold – bear in mind the pipes and filtrations system will also contain a fair volume of water, which must be included. This is vital information you will need in the future when stocking or applying treatments for the water or the fish. An inline flow meter is the easiest way – alternatively see how long it takes to fill the biggest (clean) container you have, and then time how long it takes to fill the pond. The time it takes to fill the pond and filtration system divided by the time it takes to fill your container multiplied by the volume of your container will give you the result.
The finishing touches
The important thing now is patience. If you add your fish at this stage, they are not likely to survive as the pond has not had time to develop active bacteria and the chlorine and other heavy metals present in tap water will affect the health of the fish that have established themselves. So, start up the filtration system (with the UV turned off for the first few weeks to avoid killing friendly bacteria) and apply a de-chlorinator. In a few days when the de-chlorinator has done its work and the water has reached ambient temperature, you will be able to add your first wild life. Not fish yet, but some “starter” bacteria to populate the biological filters. While you’re waiting for the big day, busy yourself sorting out the borders and adding oxygenating and floating pond plants.
A week after adding your starter bacteria you can begin to add fish gradually. If you add too many at once, the poor old bacteria can’t keep up and the resulting ammonia and nitrites can be fatal to your fish. Add the fish gradually and monitor the water condition each time. When you bring the fish home from the garden centre or specialist, they need to be acclimatised both to the water temperature and the water itself. So, to begin with, open the bag, fixing it to the side of the pond and leave it floating for half an hour or so. Avoid doing this in direct sunlight. Then start to add a little pond water into the bag gradually over the next hour and finally release your fishy friends into their new watery home.