When you have leaks in an above ground swimming pool, you can't let them go for long. Not only will the pool lose water through a leak, when a leak occurs at the seam it may expand, leading to an eventual rip in the pool's liner. Replacing the pool's liner is a substantially more costly repair than fixing an individual leak, and fixing a leak, even under the water in a pool, is simpler than you may think. Pool supply companies make leak repair kits with the water setting in mind.
Wear at least swim goggles when fixing a leak in your pool's liner. If you have a snorkel at home, this can be beneficial as well, as it allows you to stay underwater to work longer without needing to resurface for air.
Get into the swimming pool with a ruler. Inspect the leak in the seam of the pool's liner to see how far it expands down the seam. When you find the start and end points of the rip in the liner, use a ruler to measure the length of the rip at the seam. If the rip is wider than the seam, measure the width as well.
Take out the vinyl patch provided with the underwater patching kit. Measure down the length of the patch and cut a piece of patch that is at least 2 inches longer and 2 inches wider than the size of the rip in the vinyl liner. Cut the pointed corners off and round the corners of the patch after cutting it to size.
Return down into the pool with the patch that you cut and the underwater adhesive provided with the vinyl patching kit. Apply adhesive in the amount recommended on the packaging of the patching kit to the back of the patch and to the seam of the pool liner.
Press the patch into place and smooth it out so that it lies flat against the vinyl surface. Hold the patch against the liner for 30 to 60 seconds at least. Consult the packaging of your specific patching kit for the amount of time the company recommends you hold the patch against the liner.