Fixing a pond that leaks can be a difficult task. Finding a leak can prove a more elusive task than expected, and many pond owners will spend an entire season trying to track down a leak in a pond liner or prefabricated pond mold. By following a few easy steps, however, you can greatly increase your chances of finding the leak and fixing your pond.
Remove all fish from your pond. Aquatic plants can remain for the first few steps, but any fish in the pond will be under undue stress as you begin to try to locate your leak. Place your fish in another pond, or a tank with an aerator that is outdoors in an area similar in temperature to the pond they came from.
Determine the rate of the leak. You should have an idea as to how many inches the water level falls per day or per week. If necessary, use a rope with a knot per inch, tied to a stone and hanging over the side of your pond.
Pump 10 percent of the water from your pond. Once you have a handle on the rate at which your pond leaks, pump about one tenth of your total pond volume out of the pond. It is fine to estimate this number. You are trying to locate the hole in the liner or mold by narrowing down its location. After pumping 10 percent of your pond's total volume out, wait a few days and keep track of its leak rate.
Notice if the rate of water loss has substantially decreased. A small decrease may be due to a reduction of pressure on the hole, but a substantial decrease or cessation of leak may mean the hole is now above the water level. If this is the case you have narrowed down the location of the hole to a few inches around the circumference of the pond.
Work your way down until you reach the bottom of the pond, stopping when you find your leak stop-point. If the leak does not slow or cease until this point, your leak is in your bottom. Pump the remaining water out, clean out the debris, and begin looking for a puncture.
Patch the leak using approved patch material for the pond liner or mold you have. Prefabricated pond molds are typically ABS or PVC and can be patched using PVC glue or cement. Vinyl liners are trickier, and may require purchasing a patch kit from a store specializing in ponds and aquariums. Allow the patch to set before replacing water.
Refill your pond in the same way you emptied it, 10 percent at a time. If it seems the water level is decreasing again, either your patch is leaking or you have a second leak. Drain and repeat the above steps to find and patch your leak.