John,
How much water is your pool losing a day?

I just had a problem with my hydrostatic valve causing major water loss. Up to a foot a day. My pool guy actually put a plug over the hydrostatic value entry, and that stopped the leak. He said, if the ground water needs to come up thru, that the plug he put in will pop out.

One way to know for sure if you have a structual leak in the pool, or if its coming from main drain or hydrostaic valve is to shut pool off, plug your skimmers and returns , and see if water still leaks.