Usually a leak that is worse when the pump is off is a suction side leak, like a cracked pipe from a skimmer or drain. When the pump runs, it pulls the gap together and slows down the leak. It would have to be below the water level to behave this way. A typical pressure side leak gets worse when the pump is on. A typical pool structure leak doesn't care whether the pump is on or not.

Plugging the skimmer and leaving it off would be my next step. Good luck.