After getting my swimming pool cleaned up and filled with water, I quickly noticed that the water level was dropping slightly, about 19 mm (3/4 inches) every day. So I checked all the plumbing and connections from the skimmer to the filter and back through the return. I fixed a few small leaks, but only managed to improve the water loss very slightly.
Find The Liner Leak
Every time I've gotten in the pool since that day, to swim or to clean, I've been scanning the lining for a tear or some other damage. Finally, one day after removing the solar blanket and getting in, I started scrubbing the wall of the pool, and sure enough, I came up to a tiny white vertical line, about 60 mm (2 1/2") long, running along the seam of the liner and about 25 cm (10") from the surface.
Finding the leak was the most time-consuming part of this project. The repair required minimum skills and just a few minutes to complete.
Use a Vinyl Repair Kit
I retrieved my vinyl repair kit (bought way back when I first got my pool) from the "pool accessories" bin. The kit includes patch material and underwater adhesive. I also picked up a piece of wood, a plastic trowel, and a pair of nitrile gloves.
I got the piece of wood to lay on the edge of the pool so the aluminum doesn't get sticky with excess adhesive. If you use one, it must be larger than the patch and heavy enough that you don't need to worry about it moving or sliding.
With all these laid out on the edge of the pool near the leak, I cut a piece about 2" by 4 1/2" (50 mm x 115 mm) out of the vinyl patch sheet and lowered myself inside the pool.
Apply the Adhesive
As a precaution, I cut off the four corners of the patch, so they couldn't become starting points for peeling later. I laid out the patch on the piece of wood, put on a pair of nitrile gloves, and coated the surface with a generous amount of the adhesive. I tried to keep the application as even as possible using the brush supplied in the repair kit.
After covering the whole surface, I picked up the patch by each end and took it in the water without making contact with the liner yet. With the adhesive side of the patch facing the pool liner, I could then move one of my thumbs to the middle, bringing the center of the patch in contact with the center of the cut in the liner.
Attach the Patch
Applying a light pressure at this point to maintain it in place, I used my other thumb to flatten the patch against the liner—applying pressure from the center and sliding outwards to push out any excess adhesive and air bubbles.
With the patch more or less stuck to the inside of the pool liner, I slid it to get it better centered on the cut in the liner. Then, holding one finger against the top end, I used a plastic trowel to flatten it tight against the liner, at the same time squeezing out all excess adhesive, starting from the top and sliding it all the way down.
The finger at the top should keep it from shifting position during the final squeezing process. In my case, there were a few spots where the adhesive was still forming lumps along the sides, so I just pressed on the opposite side with a finger and slid the trowel sideways to squeeze out the remaining glue.
The adhesive settles quickly, so the patch should be stabilizing while you flatten it out. After that, you're all set! Just make sure you keep an eye on your water levels so you can tell if you need more patches in the future.