Well it took me a long while to do it, but I finally got around to getting some cheap Vitamin C that was mostly ascorbic acid with minimal extra ingredients (starch, etc.) and I crushed them, but them in a sock, and rubbed the stains at the bottom of my pool. Nothing happened. Tri-Chlor didn't change the stains either. I also tried rubbing the tablets directly rather than crushing them and again nothing.

I also tried this on a stain I KNOW to be metal (rust) since it is right where the metal bars are that had their insert fittings rusted from my use of Tri-Chlor in a floating feeder over a year ago and it looks reddish just like rust. The Vitamin C just didn't get rid of or even fade the stain.

So for whatever reason, it didn't work for me. Perhaps the stain is so old that it has permeated the plaster/gunite too far for the ascorbic acid to get rid of it. I'll see about getting "Jack's Magic" assuming it's more than just ascorbic acid.

Richard