I have an inground pool, about 20,000 gallons, and 30-plus years old. I've owned it for five with no issues to date. When I uncovered it to prep it for use this spring I found that it had drained about a foot down. I cannot find the source of the leak. Hoping for your help, and here's what I've tried so far:
Observe: without the pump running it definitely loses water, and given several days it always stops roughly 3-4 inches below the tile that surrounds the skimmer door. It seems to leak very little if at all with the pump running. There is no moisture near the filter pump or any above ground pipes. The automatic pool cover will short out when the pool leaks, further leading me to believe there is a leak underground somewhere. After a couple days of of the pool sitting at its lowest waterpoint the pool cover works fine.
From what I've read this makes it likely to be a suction side leak, but the fact that it leaks so far below the skimmer and that if left untouched the skimmer holds some water with the pump off makes me think that's not the case.
Tests: I have done the dye test on all return valves any small cracks around the skimmer and the vacuum port. I've also used epoxy to fill in any tiny cracks I found. No leaks identified and at least the same amount as it did prior to the epoxy fixes. No obvious cracks on the stairs or at the line where the water stops.
Leak detection companies are all quoting $350 to $750 without a guarantee to try to find the leak. Anything else I can try to find it myself? Thanks in advance for your thoughts.
to be thorough, I have plugged all of the return valves and the vacuum port, and then removing them one by one after refilling about an inch. No matter which one I removed the pool leaks at the same rate, further convincing me it's not a part of the return piping. But, I'm not running the pump at all because the water's so low, and not raising the water level high enough to be entering suction side through the skimmer, so that would tell me it's not a suction side leak.
