post winter scale on replastered pool

Help! Our pool was replastered in May of 2005. We followed the contractor's instructions balancing the water and frequent brushing all season long. During the summer, some discoloration in the plaster showed up and the contractor eliminated the discoloration in October by dropping the pH very low with slight circulation (small submerged pump) for a couple of weeks. The color faded and the pH was rebalanced by him. We double checked the pool chemistry, covered the pool the 1st week (hard cover) of November as we always did in previous years, and put it to bed for the winter.

When we opened the pool mid May, the pH was off the scale, over 8, and scale had formed over the entire plaster surface that was under water.
The contractor said he was not responsible and told us we should have gone into the winter with a lower than normal pH since the plaster was still curing. He now suggests we lower the pH (to what?) and brush the pool 2 or 3 times daily for several weeks.
Another contractor told us we would have to drain the pool, sand the plaster, acid etch the pool and refill.
Has anyone experienced this? What do we really need to do?