I asked the local pool store guy (he's the owner and seems pretty knowledgeable and he also didn't try to sell me anything). He said that it would take years for the lack of calcium in the water to cause damage to the plaster. He suggested a few weeks after filling the pool that I add in calcium based on the water chemistry at that time. He is also felt it would be easier to deal with the Calcium problem of softened water then the Iron problem of the unsoftened water. Sounds pretty reasonable, what do you all think?

JonnyG