Building a concrete koi pond is a large undertaking that is usually expensive and permanent. It's a job best suited for a hobbyist who understands the needs of koi. Still, many consult with a professional contractor or hire help for some parts of the construction process.
Mark the pond in your yard using string or paint. Include where your filtering equipment will be.
Excavate the area where you will build your pond. If you wish to build an above ground pond, this will be less tedious, but you should still make sure the ground is level.
Place your bottom drains and piping in the bottom of your pond. Many pond experts recommend using a bend connector rather than an elbow connector to connect pipes. This will be less restricting for the water flow.
Put reinforcing bars in the bottom of your pond using bricks to hold the rebar up and in place.
Prepare and pour concrete into the bottom of your pond slowly and evenly. The concrete should be leveled off at a depth of about 6 inches.
Build the walls of your pond using small, solid concrete blocks or large hollow blocks and mortar. Large hollow blocks should be filled with concrete when the walls are complete.
Install any piping or hardware you want into the wall as you are building it. This could include a skimmer or hardware to create a waterfall.
Seal your pond's interior with pond sealant or fiberglass. You can use various colors to achieve the look you want.
Install coping on the top of your walls to finish them, if you wish. You can use various materials, including concrete blocks or even large rocks to create a more natural-looking pond.
Install your filter. In the past, this often required building large chambers and elaborate filtration systems, but many modern koi experts recommend specialised pond filtration and pump systems, such as the Nexus systems sold at USA Koi (see Resources below).
Connect all of your piping tightly. Fill the pond and run the filtration system to ensure that there are no leaks. You can find an excellent graphic detailing a koi pond's plumbing at Roberts Water Gardens (see Resources below).
Test the water several times to ensure it is a neutral pH before releasing any koi into it.
For large ponds, you should consider pouring a 15cm / 6-inch concrete base under your draining system and pond floor. Also for large ponds, you might want to slope the sides of your pond's bottom so that sediment and waste slide toward the drains.
Make sure your design is solid and measurements are correct before you start working. A concrete pond is very difficult to fix or alter once it is built. Do not place your koi pond near trees. The falling leaves will change the pH of the water, and the roots could disturb your pond. Do not use a swimming pool filter and pump system for your koi pond. Because they are not used in the same way, a pool system will use more energy, which will drive up your bills. Make sure the surface of your pond is smooth, as rough surfaces can damage the fish.