A Likely Solution? I believe I have found and stopped the leak. At least for now, and seemingly for the most part. I'm posting this in thanks for those who contributed above, and hopefully to help others who may encounter a problem like mine in the future! I was loosing 4" overnight and now, it's maybe 1/4" or less overnight. (Temps here are 40-50 so evap should be at a minimum). I realize I still may have some small leaks. I spoke at length with a guy who plasters new pools professionally, asking about those hairline cracks. He said that since they were above the winterized water level, he suspected that they were due to drying out of the plaster with the water level lowered. He finds that the hairline cracks like mine usually disappear once the water level is raised, due to adding moisture back to the plaster. He said that in 20 years of plastering pools, he had only found one pool materially leaking through this kind of hairline crack. So just to be cautious, I did apply a skim coat of silicone to them before refilling, though they were not my main suspects! I got on a mechanic's creeper and spent several hours examining the tile line around this 40' pool. I found about 8-10 openings in the grout between those tiles at various places from 1/4" up to 2".I cut out the bad grout and replaced it with silicone for a temporary repair. I know that matching grout might have been better - I just didn't have any available on short notice. I also spent a fair amount of time in and around the pool side openings to the skimmers. There was some obvious missing grout there, and I did carefully seal the vertical and horizontal joints between the skimmer box and the plaster. (On my pool, that vertical joint was up inside the skimmer, maybe 4" from the face of the pool wall) I let that cure about 8 hours and filled the pool. So far it's 95% better than before! Now that I can finally keep the water level up to the skimmers, I can finally run the pump . Once we get a clear pool, I will dye test everything around the tile line, the skimmer box, and those pesky hairline cracks, just to make sure. Interestingly, in posting this on this and a few other forums, I don't recall anyone suggesting a look at the tile line. Thankfully, numerous folks did suggest having a look at the interface between the skimmers and the structure. It's a great relief so far, though I know I will have to keep an eye on things, and maybe later cut out the silicone and replace it with grout!

Care for both is nearly identical. Fiberglass can be done very quickly since there are no cure times for the shell or plaster. Fiberglass is usually a smaller pool. Larger pools may require a two piece which means significant changes in the installation process. Choosing an installer that works with you is important for both. When caring bids, make the bidders meet your specs so you can compare them equally. Try to look at pools they have done that are of varied ages on ground that is similar to yours. It's not just the pool but it's surrounding areas that shoud be noticed. Keep enough money on the back of the payment schedule to keep the builder interested in completing everything. Pool chems and energy cost every year. Repair money is a good thing to budget for too. Expect the food budget to need an increase. There will be more mouths to feed. That got me a few times. Remember, if it isn't in writing, it wasn't said. Expect the unexpected to drive anticipated costs up. Ask what it costs if water is hit during excavation before hand. Dry wells, extra gravel, big boulders and bedrock cost, sometimes dearly. What went well in other nearby yards is no guarantee that this is the case in your yard. Hope this helps. Scott

well the hole in the deep end is even bigger than the hole in the shallow end. any opinions?

With a lifetime career of constructing pools I can assure you of the following "Every pool is a great pool!!!" From the cheapest cheesiest Walmart inflatable to a poured Redimix concrete Olympic sized pool that they're all equal. Those who are in charge of them share an equal responsibility in maintaining proper water chemistry for the swimmers and staying on top of the preventative maintenance necessary to keep the pool circulatory system in proper working order. The only thing one owner enjoys over the other is a lifetime pool platform and more elbow room. I've built everything from aboveground pools, vinyl liner, fiberglass, to concrete pools. I can tell you this for fact "An inground concrete pool is a permanent swim platform when constructed properly" IMO, go with the gunite pool. I'm not going to knock a fiberglass pool, but when I dig up an old one and build a new gunite pool I wonder where their mindset was 10 or 15 years ago when they opted not to use concrete construction. I've remodeled concrete pools that have predated World War II, and removed and replaced vinyl liner and fiberglass pools that were shot within twenty. If the concrete (gunite) pool builder ahas been in the game as long as your potential builder has, GO FOR IT!!! I'd spend the extra money without any hesitation or reservations whatsoever. See ya, Kelly.