HELP! I have a 36000 gallon concrete pool. I have been losing water since I opened a week ago. This year we had to drain, replace lost tiles, fix some superficial concrete, and paint the pool. Since we refilled I have been losing water about 2 inches a day. I have shut the pump off for the past 4 days to measure the water loss. Plugged return up still lost water, main drain has been plugged for years, did dye test on skimmer, around light and superficial concrete chips and saw nothing. The water level seems to stop dropping after it hits about 2 to 3 inches below tiles. Pump is still off. Any ideas were to check next? The pool was built in the early 80s. Thank you.