I have a vinyl liner in ground pool that is 15 years old. It began leaking 2 years ago. We had 2 divers in the pool and they thought it was the liner. It would leak all the way to the bottom of the steps and quit. This summer we put in a new liner and it seemed to be not leaking. Now it is leaking again. pressure test was done on the skimmer lines and the polaris line. All tests failed. Then they plugged all drains. With the drains plugged we are still losing about an inch in 24 hours. They cannot find a leak in the pool liner or around steps that is visible. Where do I go from here is my question?