Need opinions on IG pool leak

[DistractableBoy]

When I run the main pump, I still lose water because the water returned to the pool also goes through the pipe that feeds the Polaris.

If either pump runs, I lose water. If neither pump is run, I do not lose water.

Bob

[Poconos]

Welcome to the forum Bob.
I think I would feel pretty confident about the location too. If it was a leak around the skimmer or on the suction side the situation would be reversed. Losing water either all the time or only with the pump off. As for the missing water, it could have just found a channel in the ground and is going somewhere else. I had a leak at the deep end of my IG years ago and the loss rate was about 50 GPH. It leaked for a couple weeks before I found and patched it. No trace of the missing water. Also remember that as the water leaks out it won't go uphill to the surface of the ground if that is above the pool water level. Looks like you have some digging to do. Keep us posted on the progress.
Al

[DistractableBoy]

Thanks for the confirmation of my diagnosis, Al. I am very much enjoying my membership. Much more accurate and reliable advice than I get at the pool store!

Bob