How to Build a Koi Pond

Koi Pond Basics, Safety, and Building Tips to Get Started

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

Learn more about The Spruce's Editorial Process
Updated on 11/27/22
Reviewed by
Johnathan Brewer
Johnathan Brewer
Reviewed by Johnathan Brewer
Johnathan C. Brewer II is a licensed general contractor specializing in kitchen, bath remodels, and general construction with two decades of professional experience.
Learn more about The Spruce's Review Board
Koi Pond

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Project 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 yard refresh. 

Installing a koi pond is not cheap; on average, professionally installed koi ponds cost from $10,000 to $20,000. If you have it professionally maintained, expect costs of at least $3,000 per year. Or you can do the ongoing upkeep yourself for $500 to $1,000, depending on how big your pond is and how many fish you have.

If you're making a koi pond from scratch, you can save considerable money by building one for under $2,000. The mechanical parts like pumps and filters will be your most expensive outlays. You can bring down expenses on your koi pond by planning out a smaller one, digging out the trench on your own, getting a prefabricated koi pond liner, and buying smaller, less expensive domestic koi fish that cost under $3 per fish.

Before You Begin

In the planning stages for making a koi pond in your backyard, budget out your materials, tools, and time. The larger you make it, the more expensive it becomes and the longer it takes. Expect that your pond will need to go at least 3 feet deep. You will need to plan for a water pump, filtration system, aeration, pond liner, surface skimmers, fish and food, and surrounding landscaping.

Consider building it on a hill if you want other features like a fountain or waterfall. Also, if making waterfalls, use the excavated dirt to form your cascades or contours for the waterfalls. Koi ponds don't need a waterfall, but besides looking lovely, they provide aeration, which the fish need to survive.

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 F to 77 F.

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. If the pond is deep enough, the koi will also be safer from any potential predators.

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.

Pond Circulation

All ponds require some level of dissolved oxygen in the water, especially ponds with fish. Koi fish need dissolved oxygen to breathe. Oxygen also keeps the water healthy, enabling the beneficial bacteria to break down biological wastes in the water. Oxygenated water also discourages harmful bacteria from taking over a pond. An aerated pond also helps fish breathe in winter when the top of the pond ices over.

Fountains and waterfall features are natural aerators. However, if they should stop running, it can cause a breakdown in the delicate balance of the ecosystem. Deciding whether you need a dedicated aeration system depends on how many fish you have and the size of your pond. A small or medium pond heavily stocked with koi will likely need a backup aeration system.

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.

How to Build a Koi Pond

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:

  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.

FAQ
  • Are koi ponds high maintenance?

    Koi ponds require maintenance, but they are not high maintenance. Once you correctly set up a koi pond with all the equipment, you don't need more than 15 minutes a week. Plan on feeding the fish every day and monitor their appearance and behavior. Weekly, skim away the uneaten food and leaf debris, change about 10% of the water, clean the filters, and test the water quality.

  • Do koi ponds attract mosquitoes?

    No, koi ponds do not attract mosquitoes if the water remains moving and aerated. Mosquitoes only lay their eggs in stagnant pools of water.

  • How often does a koi pond need to be cleaned?

    Complete cleaning of the pond must occur once a year. Between cleanings, you will need to continue weekly maintenance, such as 10% water changes, skimming the water surface, and cleaning the filters. The pond will be better off if cleaned more frequently, like once per season or at least once in the spring and fall.