The first aspect is location. Avoid building under large trees, this will reduce cleaning in the winter months. Garden ponds tend to look most natural if situated at the lowest point in your garden or yard. The pond needs to be deep enough to support life all year round especially when temperatures drop below freezing. There should be an area approx 1/3 of the overall base that is at least 4 - 5' deep, to shallow off if required to 2'.
There are two means to building a Koi pond . You can either dig out the area and line with a purpose pond liner, or you can again dig out the area and fit a fibreglass pond shell.
When choosing to use a liner, it will be necessary to ensure all sharp stones have carefully been removed and a protective layer of sand be placed across the bottom. Discarded old carpet laid against the side can also act as a great buffer to protect the lining. When purchasing the lining always remember to allow at least 18" overlap all the way round, this will be held in place with either ornamental stones or coping slabs.
This simple formula will calculate the size of liner required:
Take the length + twice the maximum depth + 36"
Take the width + twice the maximum depth + 36".
When fitting you will need the help of at least two other people, carefully roll out the liner and lay across the hole. One person will need to get in bare foot to push the liner into position and smooth out the corner creases. Start to fill the pond, position helpers equal distances around the pond to gently pull the liner into place. Once you are satisfied the liner is evenly distributed continue to fill the pond.
Periodical incisions can be made through the overlap between ornament holding stones for planting a few plants if the finished height is at ground level. Excess liner can then be cut away after placing the holding stones in situ. There is nothing wrong in building a retaining wall should you wish to have the pond raised, or you are building on an existing concrete base. Just ensure the wall will be strong enough to take the weight of the water (if unsure consult a builder).
Using a pre moulded fibreglass pond will have to be placed to sit snugly in the dug out area and finished to ground level. Lay the mould upside down and mark out the area to be excavated allowing approx an additional 6" all the way round to manoeuvre the shell into place. As with the liner it's advisable to lay a layer of sand on the bottom to act again as a buffer. Back fill and gaps remaining after the pond as been fitted to ensure adequate support for the frame.
Once the main pond area is completed you will need to calculate the volume of water it holds to know the size of filtration system and pump you will require. Fibreglass ponds should be supplied with this information. However if you have built your own pond you will need to do a little arithmetic.
This simple formula will calculate the volume of water in your pond:
Length x Width x Average Depth x 6.24 = Volume in Imperial Gallons
Length x Width x Average Depth x 1000 = Volume in Litre
Length x Width x Average Depth x 7.5 = Volume in US Gallons
Once you know the size of your pond, file this info somewhere safely, if ever in the future you need to add any treatment to the water you will need this information.
You will now be able to purchase a filtration system and pump which will be correct for your size of pond. All good aquatic centres will be able to offer you different products according to your needs and budget.
One of the most important points to now make here is, OK you have your pump, your filter system and your pond up and running, but as most Koi keepers will tell you it's vital to have good water. I would recommend no fish be placed in the pond for at least 4 weeks, this will allow your filtration system to mature and the water to settle. After this time start by introducing just a couple of very small Koi and keep a very close watch on their health for a few weeks. It's not a bad idea to purchase a water testing kit, and take samples and test regularly to make sure the water is good.
I was once told, we don't keep or look after the fish, but we are keepers of water. Get that right and you will have Healthy Happy Koi.