stain...iron? in new pool

[mneal]

We have a 5 month IGP (I am newbe) and we had a mustard algae issue about 1 month ago because I slacked on the chlorine. I shocked, brushed and added lots of chlorine (some stop yellow from PS). Algae all good now. About a week ago I noticed a rust colored stain in hot tub. I scrubbed it with Cl puck and had no effect....not algae. I just sat a Vitamin C tablet on the stain and the tablet made a big on it's own that is much worse. :-( Yikes, I saw people talked about putting tablets in a old soak and scrubbing with it but I was in a rush and was in street clothes and I thought I read about letting tablet sit on stain. Did I dream that? D id I screw up big time? Oh the water chem from PS water test 2 days ago (Order Ben's kit about 6 wks ago and waiting on it yet:
TC: 3.0
FC:3.0
pH: 7.6 (I added 1 cup acids since)
TA: 80
Cal Hardness: 220. (I added ~2 lbs calcium since)
Stab : 50
TDS: 650
Cu: 0.3
Iron: 0.1

Thoughts from the pros?

Next day UPDATE:
I woke up this am. to find the "new" stain that the ascorbic acid tablets (Vitamin C) made are gone. I guess the CL bleached them out? I dunno , but am obviously happy they are gone. I think the original stain is somewhat better right by the tablets. So the stain is metals for sure right.......should I put a bunch of them in a soak and scrub away?