Alright, I did a little *research* and read about a "vitamin C test" to see if ascorbic acid is what I need...
I took a handful of Vitamin C (chewable orange juice tablets) and put them in a white sock and secured it with a rubber band. Then I used a hammer to break the tablets down to a large gravel (not powder). I then tied this sock on to my pool brush and used the brush to hold the sock against the stain for 30 minutes.
There doesn't appear to be any difference in the stain!

Now, does that mean I do NOT need to use ascorbic acid or was that a total waste of my time (and my expensive Vit. C tablets)???
HELP! I don't want to spend any more money on this than I have to...