Granite Pool Wall - Calcium?

Hi - We have a pool that was dug into the side of the hill in our back yard.  As a result, we have about 3 feet of raised wall above the pool on one side which we covered in beautiful granite.  A few years later the granite is not so beautiful . it has white streaks and in some areas a significant buildup of white "chunks".  We assume this is calcium build-up.   Any suggestions for how to clean?  We have estimates from a tile cleaning company for $700 to shoot glass beads at it ... looking for something a little more economical.  Help - we have a party at our house in 4 weeks and our granite wall is embarrassing.