Ponds can be a beautiful feature to any garden, whether they house plants or fish. They do require some maintenance. Sometimes, even with the best care, they spring a leak. There are a few tricks to make finding the leak as simple as possible. If the leak is near the top of the liner, you may not even need to remove the plants or fish. Once the leak is found, you can purchase a repair kit at a local hardware store
Turn off the pump to your pond and allow the water to continue leaking. If you do not lose water from the pond at this point, you know the leak is not in the liner but somewhere in the tubing.
Remove the plants and fish if the water level drops too low. If the leak is somewhere near the top of the liner, you can skip this step.
Wait for the water to stop leaking. Once it has stopped, inspect the liner along the water level. Look for any irregularities in the liner that could be the source of a gash or hole. You may need to scrub off algae with a cleaning brush to get a good look.
Fill a spray bottle with milk and squirt it into the water next to the liner. The milk will act as a tracking device for water flow. If your liner has a fast leak, the milk will immediately get pulled through the hole with the water. This technique will not help you find a slow leak, however, because the milk will disperse too quickly into the water before flowing out. So, if you have a slow leak or no leak in the area you squirt the milk, the milk will simply turn the water cloudy.