I just moved into this house and inground pool maintenance has quickly become my new hobby/obsession. My pool holds about 10,000 gallons. Running the filter for 4 hours, dropped the water level about an inch. Obviously, not a good thing. I left the pump off for a day, and had barely any water loss, so I know it's a plumbing issue. Problem is, I don't see any leaks! I assume that means I'm losing dozens of gallons of water underground. That scares the bejeezus out of me. Is my assumption correct? Is there any other diy troubleshooting I can do or do I need a pro? Thanks for your help!