Creating a backyard pond with a fibreglass or plastic preformed pond shell is an inexpensive way to add a dramatic focal point to a garden. Easy to install in a day, they provide instant pond gratification. Depending on the manner in which it was installed, or the soil it was installed in, a preformed pond liner may stay in place for years, or it may begin sinking and becoming uneven within days of installation. Proper installation of a preformed pond shell will reduce the possibility of having to fix a problem with an uneven pond down the road. An uneven preformed pond cannot be fixed without removing it and beginning again.
Fill the large bucket or children's pool with water from the pond. Remove all submerged, marginal and floating plants from the pond and place in the bucket. Remove all fish from the pond with the fish net and place in the bucket with the pond plants. Move the bucket to a cool, shady location out of heat and sunlight.
Turn the pond pump off and disconnect the filter. Turn the pond pump on and place the pump hose in a garden area to drain. If there is no pump in the pond, use a large bucket to remove the pond water. Remove as much water (possibly even all of it) as needed until the pond can easily be removed from the location.
Add a layer of sand to the bottom of the hole, filling in any sunken areas. Tamp down firmly with your feet or the back of the shovel. Place the carpenter's level on the sand, adjust, and tamp until level. Sprinkle the sand with the garden hose gently until wet, then tamp and check level again. When level, replace the preformed pond shell. Place the board across the top of the pond and check to make sure it is level. Backfill where needed on the bottom or sides until the pond is level.
Fill the pond with 2 inches of water and let sit for an hour. Check for level. If level, add 2 more inches and check again. Fill the pond until 2/3 full, de-chlorinate if needed, and allow to sit for the recommended product time. Add the pond plants back into the pond first, then the reserved pond water and fish.
Save as much of the old pond water as possible to add back in to the newly levelled pond. Keep fish and plants out of the sun and in a cool place. Use a pump to give the fish oxygen if they will be out of the pond for more than four hours. Cat litter can be used if no sand is available for levelling.
Keep fish away from curious cats or other predators while the pond is being levelled.