YT: Pleats or bubbles under the pool liner are usually caused by groundwater seeping underneath the pool and pushing up on the liner. When groundwater rises too quickly, it will put pressure on the pool base and your liner will float. As groundwater builds up and seeps through the concrete, air enters behind the liner, causing air bubbles and pleats.
You can and should control groundwater levels before any air bubbles or pleats appear, for they might weaken or damage the liner. Check the dry well frequently, particularly in the spring and fall when there are heavy rains.
Once the pool is closed for the winter and the water level in the pool has been lowered, it is even more important to control groundwater levels.
The water level in the dry well should be kept lower than 18 inches. If it is higher than that, drain the excess with a submersible pump. Don't simply drain the pipe in the dry well, but all the water around the pool as well. In some cases, that may take hours or days.
