Have aged in-ground pool with concrete and plaster walls that were surfaced with fiberglass. Portions of the top 1-2 feet of the fiberglass and plaster were in poor shape. I had the top foot of the fiberglass and plaster removed around the entire pool and a new coat of plaster applied. A pool fiberglass contractor removed the remainder of the fiberglass to a level of 3-4 feet from the top, and was supposed to install new fiberglass from that level to the top of the walls, all the way around. He did what seems to be a largely OK job about half-way around, and "hung" the fiberglass around the other half, but didn't apply the last and most important resin coat to that half and maybe other coats as well, which were what was going to harden and make the fiberglass impenetrable by water. Now, I am having to add 150 to 300 gallons of water every few days or every week, which I never had to do before. I'm not sure where the water is going. The only other thing that was done is that before re-filling the pool, I installed a new screw-in plug in the relief opening at the bottom of the main drain. The diameter of the top one eighth inch of the new plug was 1-2 inches greater than the diameter of the threads, forming a sort of cap and creating a positive stop, and there was an o-ring around the top thread that rested against the underside of the "cap". As an extra measure, I put several wraps of plumbers tape around the threads right up to the o-ring. I screwed the plug in by hand, and lightly seated it with a plier. At that time, I felt confident water could not escape through the relief opening.
Questions:
1. Might water be escaping through the relief opening despite the capped, o-ringed & taped plug?
2. Can water from the pool be escaping through the plaster and concrete walls where the last and possibly other coatings of resin were not applied to the fiberglass?
3. If the pool water I am losing is passing through the walls where they are not protected by finished fiberglass, what damage to the walls or other problems can that cause?