I'm sure my problem is simply the sand underneath NOT being wet enough and compacted enough. I watched the installer as they spread the sand. I did not think they watered it near enough (it was dry sand) and they didn't spend much time tamping it down. The sand cove has settled a lot also.
I would like to know if anyone has had good luck with foam between the sand and liner or a Gorilla Pad or similar and foam coves also? And also, has anyone used PoolCrete under an AG pool and what kind of expense is that?