I am in no way an expert on this, just a frustrated 'stain scrubber'.
I went ahead and drained and acid washed my pool last Friday. It looks like new, no more stains, and it was very easy. Cost me about $150 bucks for a 25,000 gal in-ground pool. I KNOW I would have been sold at least that much in chemicals in an effort to 'lift' the stains without draining the pool.
I was very suprised to find that when I started to do the acid wash, when I compared a section just washed to a yet to be washed area, it was obvious that over the years my pool had experienced some 'metal' staining issues..... light green/teal colored stains covered the entire pool surface.
Of course, the acid wash also removed the 'sand colored' stains, which I believe were a darker copper stain that I precipitated into the plaster by just throwing a bunch of shock into the pool upon opening, without first testing the water for balance. My bad.
Good Luck with whatever you decide to do. IF you decide to treat the stains with chemicals after filling.... AND HAVE SUCCESS, would you mind posting back so we all can learn what worked?