I'm a pool newbie with a very old (21yr) pool. I noticed that my pool automatically reduces the water level so I asked the pool store about it. She said some of the older construction have built in overflow and told me to look in skimmer for hole or pipe. I found nothing there but do see a 2-3 inch linear opening that is very thin in the tile under lip of pool. Could this be where my pool is draining? If so the water is just going into the ground, couldn't that cause setteling of the earth under the pool and subsequently damage the pool?