Well, I had a real "Aha!" moment when I put the Vit C against the stain. I came away clean as a whistle! That's why I love you all on this forum. I'd be totally lost about this pool without you guys.

An interesting thing also happened while I was in the pool trying out the vitamin C.

I have tried using a scrub sponge in the past with zero results. Today I accidentally brushed my foot along the coping edge and noticed that some of the stain came off so I tried the sponge on it.

I made my way all around the 16 X32 using my foot and the sponge (got lots of aquatic leg lifts in today!) and found that some of this stuff comes off down at the bottom of the pool. It didn't at all farther up the wall.

When I took the sponge out to look at it, there was rust colored stuff on it that rinsed out. Is this still metal too or do I have some algae?