If you suspect your pool liner has developed a leak, you can locate it using food coloring. This may take a bit of searching, but this is a relatively straightforward process:
First, ensure the pool is full just in case the leak happens to be above the current water level.
Then, you’ll want to enter the pool, using your feet to feel around the pool’s floor. If you feel a squishy spot under your feet, this may be an indication that the leak could be coming from the bottom of your liner.
If you do not feel any indication of a leak coming from the bottom of your pool, simply begin placing a few drops of food coloring around your pool’s perimeter. The food coloring is used to let you see the flow of water.
Continue placing food coloring around your pool until you have located the leak. Once the food coloring is dropped near a leak, you’ll be able to see it flowing out of the exact spot the leak is located.