A preformed children's swimming pool is very similar to a preformed pond liner. They both hold water and can be placed in the ground to form a pond but a pond liner is going to cost you triple what a kiddie pool costs. As long as you don't mind the colouring of the children's pool or the perfectly round shape, you can use the children's pool as the liner of your fish pond. Since children's pools are only a few inches deep, the pond would be well-suited for small goldfish called comets. Comets are smaller than most pond fish and are easy to care for.
Purchase the deepest preformed plastic children's swimming pool you can find, if you're not using a kiddie pool you already have. Purchase a pond pump at a pond supply store or home improvement centre that is recommended for the amount of water your pool holds and is safe to use with fish.
Dig a hole the same depth and width as the preformed pool. Remove all rocks and other sharp objects from the hole.
Tamp the soil down so that is completely level with a hand tamper. Make sure the bottom of the hole is completely level; an unlevel base will not allow the pool to be filled evenly.
Set the preformed pool down into the hole so the rim is level with the ground. Pour a thin layer of pond or aquarium gravel into the bottom of the pool.
Fill the pool with water. Set a pond pump into the pool with the cord running out of the pool to an electrical socket. Follow the manufacturer's instructions on where to place the pump.
Set a variety of different aquatic plants into the pool. Place a few comet gold fish into the pool. Place 3 to 6 fish into a pond that is 4 to 8 feet in diameter.
Feed the fish gold fish food daily and keep the pond pump running so the water can oxygenate. Add more water to the pond as needed.
Clean pond regularly to keep your fish healthy and the water clear. Do not put koi or carp into your pound, because they require more water than provided by your pool to survive. Follow the manufacturer's directions on how to use and care for your pond pump.