There are several cracks that are running through the plaster/tiles in the pool and it feels like they are larger this spring. I did the dye test and there is no water leaking into the crack. I had 2 pool builders check them out in the fall. The first one said that he needs to take the coping off and rebuild the shell and replaster, but had no idea what has caused the cracks, hence no guarantee whatsoever it won't happen again. BTW, he was the same guy that apparently repaired the pool a year before we purchased the house, so 5 years ago. He was very evasive on what was done, but from what I can gather, the curved corners were rebuilt, the pool replastered and all new coping was installed.
The second guy thought that the cracks are due to the surrounding soil pushing on the shell, especially during winter, when everything is frozen and expands? However, he was confused about that a bit, because the ground slopes away from the pool. There is some movement on the concrete deck, one of the blocks? is a bit out of the ground right next to the coping. So I guess that is a possibility too. His solution was the same, and he also would not guarantee that won't happen - he suggested to consult a geologist?
Does the fact that the dye doesn't seep into the crack mean that the shell is fine and the cracks are only superficial on the tile and the plaster? What is the best course of action here to repair and possibly prevent this from happening again?