How to build & seal a wooden koi holding tank

Updated April 17, 2017

A koi holding tank, or koi pond, is a beautiful and unique type of water tank to hold koi fish. If you have an empty corner in your backyard or alongside your patio, you can build your own wooden koi holding tank. Decide how big you want your tank and which type of wood you'd like to build it with. Buy the wood from a lumberyard or building supplier. After your tank is finished, enjoy stocking it with beautiful koi.

Place the posts of wood on a flat concrete surface where you want to build your koi tank. Position two long posts parallel to each other and two shorter posts parallel to each other, to make a rectangle.

Pre-drill holes for the spikes on every piece of wood with an electric drill. Space the holes every foot apart. Insert dowels into the holes.

Line up the wooden beams evenly and stack them on top of each other. The holes on one beam should slide right onto the dowels of the beam below it.

Lay as many layers of posts as tall as you'd like your koi tank to be.

Put a tube of pond sealant into a sealant gun. Place the tip of the tube along the bottom edge of the tank along the floor on the inside of the tank. Squeeze the handle of the sealant gun and apply a line of sealant along the bottom edge of the tank. Apply a line of sealant along all joints inside the tank.

Place a pond liner inside the tank. Climb into the tank and fit it into the shape of the tank. Allow the extra length of the liner to fall over the outside edges of the tank.

Place a garden hose inside the liner. Turn on the water and fill the liner with water. The weight of the water will pull the liner down into its optimum shape inside the tank.

Stand outside the tank and pull the edges of the liner out toward you. Cut the liner to fit neatly over the edge of your tank, using a scissors.

Place thin planks of wood on top of each side of the tank, pressing down on top of the edges of liner. Attach the top planks to the tank with an electric nailer and 3-inch nails.


Enhance your koi holding tank with plants and flowers.


Wear eye goggles when using electric drills.

Things You'll Need

  • 1 by 4 cedar posts of wood
  • Electric drill
  • Spikes
  • Pond sealant
  • Sealant gun
  • Tape measure
  • PVC pond liner
  • Scissors
  • Garden hose
  • Water
  • Electric nailer
  • 3 inch nails
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About the Author

Based in New Jersey, Robert Raphael has been writing health and technology articles since 1993. His work has appeared in “Natural Living” magazine and “Extreme PC” magazine. Raphael received the Jonathan Melman Literary Award in 1994. He holds a Bachelor of Arts in journalism from Brandeis University.