Mbar is the metals expert here, and I'm not questioning what she is telling you at all. I just want to point out that sometimes you can eliminate the metal stains without the ascorbic acid treatment. I have iron in my fill water, and have had staining a several times. My stains have always lifted with the use of the metal sequestrant alone. It's worth trying the metal sequestrant alone first, making sure that you put enough of it in to keep all of the metal in solution. You will need the metal sequestrant anyway, even if you use the ascorbic acid for the stains.

My pool is vinyl, I'm not sure if that makes a difference. I suspect that the age of the stains plays a part too.....if they are relatively fresh, the sequestrant alone is more likely to do the job.