It's now approaching 36 hours after the above treatment, and the stains have not budged!
Last night, I was starting to wonder if the vitamin C would do anything at all, so I picked the three worst stains, and directly applied vitamin C using a sock. Here's the before (note this picture is before my initial treatment with "iron and cobalt remover" so many of the stains you see here won't be in the next pictures, but the stains I chose are the most persistent/darkest):

You can see they are "streak" pattern stains where they are sloping down the slope from the shallow end to the deep end.
Here is what they look l after I've applied the vitamin C sock to 1 and 2 (with 3 actively being covered by the sock. The stains turned from greenish brown to brownish purple and look overall worse! (nighttime picture taken with pool light on)

This picture I took the next morning before dawn (today!)

The stains are noticeably lighter overall compared to before the sock treatment, and the brown/purple parts are only minimally brown/purple, and I couldn't get a good picture of stain #3.
Which makes me feel pretty confident that the vit C should lift ALL the stains. However, the rest of the stains haven't budged! I'm considering adding more vit C tonight, perhaps with the pump turned off so the vit C can settle on the bottom of the pool directly on stains, then waiting 30-60 minutes and restarting the pump. The problem with this method is I have stains on the walls too so they won't be touched by directly applying the vit c to the entire bottom of the pool. Also the vit C likely will dissolve before getting to the bottom of the deep end.
Another alternative is just to dump a few more pounds of Vit C into the pool while the pump is running and see what happens. Any thoughts?
And as for the bottom of my "pool fix list", yes, I'm definitely getting there!
Thanks again!