Thanks for your quick reply.
Morning update - pool is clear as a whistle. DE filter filtered all the green out over night apparently. Stains on bottom of pool remain.
Source of pool water - well water. I have had the pool for years and years, no metal issues. Whenever pool gets low, which is happening often lately, I fill with hose water (well water).
When I went in for the stain initially, they sold me "Green Away" - which is like a super duper shock apparently... I will call the store when they open and see what the ingredientas are exactly.
A week later, I went to another place because of stain. They assured me it was NEVER mustard algae because that algae is easy to brush off and this stain was not moving with brushing. They checked my water - everything good for treatment - sold me Phoenix Super Erace (Highly concentrated formula removes sequestering and chelating metals (iron, copper, manganese), removes metal stains, restores water clarity as well as reduces scale formation on pumps and heaters. Super Erace works by forming a clear insoluble crystal with the metal ions normally found in the pool. These insoluble crystals are then removed by filtration) http://phoenixproductsco.com/metal.cfm
When I shock, I use 3 lbs of HTH Super Shock.
I am hoping and praying that the staining on bottom of pool is metal related and not mold... does the green after shocking signify to you that it is metal related?