Ksturge,
You can use any stain treatment that you can get at a pool store. It's just that ascorbic acid is cheaper. If you want to, you can try to get rid of the stain by bringing down your ph to 7, and using a sequestering agent like Metal Free or sequasol, or Jack's magic. Put in at least what it calls for on the bottle, and maybe a little more. Keep your filter on 24/7. Sometimes stains that aren't too set in can be lifted off without a stain treatment - but it doesn't always work. But you can try it first, and if it doesn't work, do the stain treatment.