On Sun, 18 Jul 2010 10:26:00 -0400, "Don Phillipson"
wrote:

Our well water has high levels of calcium and some
rust. So, while the pool is clean and chemically
stabilized, still water overnight reveals next morning
ultra-fine yellowish powder on the bottom. It is so fine it
goes straight through the sand filter and back into
the pool, making the water cloudy and greenish.
Is there any cure for this, perhaps by causing the
dust to agglomerate so that the sand filter holds it?

You might find a flocculent that will stick the "dust" together so your sand
filter will grab it, but that's the problem with sand filters. The real
solution is to replace your sand filter with a DE filter. That solved a bunch
of problems for us.