How to Build a Koi Pond

Koi Pond

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Overview
  • Working Time: 5 days - 1 wk
  • Total Time: 1 - 2 wks
  • Skill Level: Advanced
  • Estimated Cost: $1,000 to $2,000

It’s said that koi bring prosperity and good luck. True or not, what is certain is that koi will bring a splash of swirling color and a serene presence to your yard. Because koi are so hardy, maintenance is minimal. Learn how to build your own koi pond for a near-instant yard refresh

Basics of Building a Koi Pond

With a koi pond, you’re building not just a garden pond but a habitat for living creatures. The needs of the koi determine many aspects of the pond itself.

Pond Depth

Though classified as coldwater fish, koi don’t necessarily love cold water. Nor do they do well in very warm water. Keep the water temperature moderate, from 59℉ to 77℉.

Correct pond depth helps the koi regulate their own temperature. The koi pond should be at least 3 feet deep so that the koi can descend and stay cool in the summer. 

Pond Dimensions

Big fish need a big pond. For around five koi, your pond should be 1,000 to 1,500 gallons, minimum. Ten or more koi will need double that capacity: more than 3,000 gallons.

Visualize a 3,000-gallon pond as a space that's 18 by 24 feet, with a depth of 3 feet. Scaling down to a 1,000-gallon koi pond, you still need to maintain that 3-foot depth because koi need deep water. With that depth, the dimensions of the pond would be 6 feet by 8 feet.

Pond Location

Picking the right location for the koi pond is important for the health of the koi, as well as for water quality and your enjoyment of the pond.

Keep the pond relatively close to the house so that you can bring the hose from the house's outside faucet over to the pond. The side of the house also provides access to an exterior electrical outlet. Keeping the pond closer encourages regular maintenance.

Consider the balance of sun and shade throughout the day. Ponds in full sun grow algae faster than ponds in shaded areas. For the sake of the koi, too, it's good to keep the water temperature moderate.

Safety and Permitting

Before digging, call your local utility location service. Water, gas, electrical, and sewer lines are a minimum of 12 and 24 inches deep. Given the depth of the koi pond, the likelihood of inadvertently hitting a hidden line is great.

Small fountains or garden ponds may not need permitting, but a koi pond's large size might require permits. Most types of plumbing and electrical work require permits.

What You'll Need

Equipment / Tools

  • Shovel
  • Marking paint
  • Garden hose
  • Tape measure
  • Backhoe (optional)

Materials

  • 45 mil EPDM liner
  • 4-inch flexible hose pipe
  • 4-inch drain
  • Decorative stones
  • Settling chamber
  • Mechanical surface skimmer
  • Biological filters

Instructions

  1. Lay Out Pond

    Lay out a garden hose on the ground to trace the rough outlines of the pond. Generally, you'll want to scale the pond upward to accommodate the fish as they grow. This also builds room in case you add more koi. Experiment with various shapes.

  2. Dig Pond

    Dig the pond by hand or with hired heavy equipment to the required depth. Rather than creating tall sides, terrace the sides by about 5 to 7 inches per step.

    Tip

    Due to the sheer scale of the koi pond, it's highly recommended that you hire a person or company to use a backhoe or mini-excavator to dig the hole.

  3. Add the Drain

    Trench out the pond to create a drain at the pond's lowest point. Run the flexible hose pipe.

  4. Add Pond Liner

    With a helper, unfold the EPDM liner and fit it close to the contours of the pond. It helps to do this on a warm day, as the EPDM will be more pliable. The liner should extend onto the banks of the pond by at least a foot.

  5. Add Stones

    Lay down smooth stones along the bottom of the pond. Place larger flat stones on the bank to hold down the edges of the liner. EPDM deteriorates faster when subjected to sunlight, so be sure to cover all exposed sections.

  6. Install Setting Chamber

    The pond's drain pipe runs over to and up into the settling chamber. The settling chamber should be on the surface and can be hidden behind plants, rocks, or an enclosure.

  7. Install Water Pump

    Purchase a pump with a gallon per hour (GPH) rate that equals half or more of your pond water volume. This ensures that the water will recirculate every few hours. The pump should be submerged. The unit pumps water to the settling chamber.

  8. Fill Pond With Water

    Use the garden hose to fill the pond with water. Keep an eye on the pond so that it does not overflow.

  9. Add Mechanical Surface Skimmers

    Electrically operated surface skimmers mechanically separate small pieces of debris from the water. Some of these skimmers float on the surface or are installed off to the side.

  10. Add Biological Filtration

    Biological filtration methods balance out the aquatic system by breaking down or slowing unwanted biological growth. You have a wide range of biological filtration options that include plants and animals:

    • Roots in submersible tubs
    • Lily pads
    • Water lettuce
    • Waterweed
    • Smartweed
    • Snails
    • Frogs
    • Birds
    • Bats
  11. Introduce Koi to Pond

    First, place the koi in bags containing the pond water. Let them acclimate for about 15 minutes. Place the bags in the pond water and let the fish swim out.

    Add just a few fish to the pond at a time, no more than five or six in the 5- to 6-inch size range. This lets your biological filters adapt to the koi. Keep a close eye on the koi in the first week or two for parasites or any biological problems.