How to Build a Koi Fish Pond

Two Methods:Pre-made pondDigging own shape of pond

Koi and other goldfish can grow very large, sometimes reaching lengths of over 3 feet (0.9 m)! They're best housed in large ponds with a TON of filtration and weekly water changes. With the right size pond, filter and other equipment, caring for koi and goldfish can be lots of fun.

Method 1
Pre-made pond

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    Buy all your supplies. These are listed below under "Things You'll Need". You might want to hold off on the koi until the pond is ready though, especially if you're slow at digging and don't foresee completing this project in an afternoon!
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    Measure the plastic pool as best you can using a measuring tape.
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    Dig an appropriate hole for the pond, going by the measurements you've made. Choose a flat, available area of soil.
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    Place the pool into the hole. Make any adjustments needed and fill in any extra space or make more room if the pool doesn’t fit. Make sure all the outside of the pool is closed in and no longer visible.
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    Spray the inside of the pool with the protective spray. Wait for about 5 hours to dry and set.
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    Fill the pool up with spring or fresh water till it is about 80% filled. If you do not have spring water, put tap, well, or city water into the pool about 80% and put several drops of dechlorinator and mix with pool net.
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    Fill the pool with the gravel and spread it out evenly across the bottom.
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    Put about 1 ounce of beneficial bacteria in the water. Wait one hour for it to settle and spread.
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    Place the plants in the desired location.
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    Add the filter to the water. Wait about half an hour for the water to adjust with its new content.
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    Place the koi into their new pond. Sit back and enjoy!
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    Koi fish deposit a large amount of waste into the pond so if you want the water to be clean and clear then you will need to add a filtration system that consists of a pump and a filter. In the case of larger ponds an ozone generator system may also be required
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    Traditional swimming pool silica sand filters are not a good choice to use for Koi fish due to the volume of waste plugging the sand filter. A cartridge or bio filter are a better idea for koi fish ponds
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    Ozone is an oxidizer and a chemical free sanitizer in ponds. While waterfalls do add oxygen to the water a high output ozone system can keep the water completely clear and clean.
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    Be sure to separate the suction points for the plumbing system. Having multiple suction ports for the pump in the water will prevent an entrapment hazard that could harm the koi fish.
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    In the "Things You Need" section below, I suggest using a floating filter to clean the pond. This is more of a cheaper filter then a quality filter but it still works well enough to keep the pond clean for a short time. The above suggestions would work best.
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    Golf ball snails and bottom feeding fish can help to process algae from hard to clean surfaces like the gravel bed floor. Snails reproduce very quickly so keep an eye on the snail population to avoid being over run.
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    Pre-made ponds come in a thin black plastic and thicker acrylic resin materials. While both will work for pond you should use the thicker acrylic pond if you can find one as the floors are many times thicker and less likely to develop damage or leaks

Method 2
Digging own shape of pond

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    If you can't source a suitable pond or you just don't like the shape, here is an alternative method.
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    Select a suitable area of the garden. Map out the exact shape you'd like the koi pond to form using markers.
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    Dig the shape out. Have a helper if you've made this a large area. Be sure to include terraces to gently slope from the surface edges to the deeper part of the pool.
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    Line the dug-out area with sand and paper. Newspaper is fine to use.
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    Place a tarpaulin over the top of the newspaper and sand lining. Have the tarpaulin come up and over the edges. If it's windy, keep it in place using rocks or other weights.
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    Fill the pond with water. Follow the steps above for suggested water usage.
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    Finish the edges. Edge with rocks to beautify the pond and to hold down down the edges of the tarp.
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    Add the koi. Sit back and enjoy.


  • Try to stock as few fish in your pond as possible.
  • Birds of prey can be a detraction to a Koi pond. If this is a problem then you can stretch netting or chicken wire over the pond to protect the fish, but if this is not an option then hanging strips of tin foil directly around the pond will deter birds.
  • You can also add water lilies to add flare to your pond.
  • You don’t have to have Koi in your pond. You can have goldfish, tetras, or turtles! Just make sure the pond has a land surface if you have turtles.
  • If you want your fish pond to have a different color, you can color the inside of the pond with spray paint before the protective paint!


  • Koi and goldfish create a lot of waste so monitor your water carefully.
  • Keep your pond away from harsh sunlight.
  • Do not put rocks in the bottom of your pond. Food and waste will accumulate in the spaces and you will have a cesspool instead of a pond.
  • Place mesh over your pond if there are animals trying to eat your fish.
  • If it rains, cover your pond with a tent that has access to air.

Things You'll Need

  • A pond large enough to hold 2 gallons (7.6 L) per inch of adult fish.
  • Koi or goldfish food
  • Powerful filtering system
  • Large air pump
  • A wading pool
  • Anacharis plant
  • Java fern
  • Gravel
  • Floating filter
  • Beneficial bacteria
  • Protective paint
  • Spade, newspaper, sand, tarpaulin, rocks

Article Info

Categories: Goldfish