It is not uncommon to hear customers worry about pond leaks. There are steps that you can take to help find the source of the leak. The internet tells pond owners to add milk to the pond . . .please don’t believe everything you read on the internet! We have yet to determine a leak with the help of milk:o).
First, fill the pond up to the ideal level. If you have a skimmer, this is typically the second from the top screwhead on the skimmer faceplate. Turn off all pumps and fountains. Do you still lose water? How much in what time period?
Refill the pond up again to the ideal level with one pump running? Continue to do this with each pump.
If the pond only loses water with the pumps on, you can start looking for depressed liners in the pond creek and waterfall areas. Check your biological waterfall box, if you have one. They will sometimes overgrow with aquatic plants and dam up the front of the box causing water to spill out the back of the box. Once the obvious is checked, you can check tubing. Spiral tubing tends to crack between the ribs causing leaks.
If the pond leaks even with the pumps off, you need to consider a damaged liner. Check for vermin damage, sharp object damage, and box connections. Liner can be patched using a liner patch kit.
It is common for ponds to lose 2-4 inches of water a week due to evaporation. You can replace this by using a hose or by use of a pond water autofill.