Understood. If I'm tracking, the pool doesn't leak when the pump is off and skimmer/returns are plugged. As stated earlier, at least you know your next test cases:
1) Pump OFF (skimmer/returns NOT plugged)
2) Pump OFF (skimmer/returns plugged) to see if you can duplicate the winter results
Ok, summer is nearly coming to a close. I've been maintaining our water line by adding about 4-5 hours of hose water every 2-3 days, but this leak is still very active. So i've taken your suggestion and tried it out. Heres the results...
1. Left all returns/skimmers open. SHUT OFF the pump. (See First Image)
- 1st Tape Line: Aug 22, 6 pm, the water was at the bottom of that tape
- 2nd Tape Line: Aug 23, 6 pm, the water was at the bottom of that tape line (about 1.5 inches of loss in 24 hours)
2. At this point I plugged all returns/skimmers. Pump remains OFF.
- Aug 24, 12 pm, the water has dropped another 1 inch below the 2nd Tape Line (See Second Image)
- 3rd Tape Line: Aug 26th, 6 pm, the water has dropped at least 2 inches further (See Third Image).
At this point, the water line is below the Skimmer boxes. Its back up in the 90's again so I need to get the pump running before this thing explodes with Algae. The skimmers remain plugged (and the skimmer valve closed so its not pulling air). I reopened all the returns so the pool is running off of just the main drain intake and all returns are once again open to allow some circulation to rebalance the water.
I will run it for a few days to get it the chemicals balanced, but I'm not sure whats left to test. Pump on is losing water. Pump off is losing water (whether returns/skimmers are plugged or unplugged). This is a new problem now, because as I mentioned in my previous posts. When i plugged everything last fall, the water loss stopped.
I am considering bringing out another leak detection service to scan the pool with hydrophone so see if we can locate this thing. But i'm very close to renting a bulldozer and filling this thing in with dirt

Incredibly frustrating.
I'll add that through these 5 days of testing with the pump off, there is no water or wetspots anywhere around the yard, equipment, nothing. Where the heck does nearly 5-6 inches (in a 26k gallon pool) go without being visible!