Quote Originally Posted by MyBlueDog
Ok... I plugged the main drain for 24 hours using one of those PVC plugs with the wing nut on it that I got at Home Cheapo, and still I have over 1/2 of water loss.

So much for my theory that main drain was leaking and the crete was put their on purpose.

I'll plug the skimmer also and see if that slows it down.

Speaking of "slow" --- a slow process of elimination, huh?
Dog, 'slow and steady wins the race' Finding a leak in a pool is an inexact science, but doing a 'process of elimination' will eventually find the problem. You are fortunate in that you dive, hiring a diver is $$$. If you chip away at it slow and steady, you'll save yourself sooo much trouble.
1st step is to do a vessel test, plug off all inlets and suction ports (using the bucket as you've done) and check the bucket vs pool loss. If no discernable difference is detectable, the leak is in the lines and that's where you need to focus your attention. Pressure testing each line isn't too hard and can further isolate the leak. Should you need more specifics, don't hesitate to ask, you seem to know the drill, so I'm not bothering to get too specific. Happy Mem Day!!