I have some organic stains that respond to chlorine pucks, and so have been superchlorinating the pool for about two weeks with liquid chlorine. The stains may have lightened a bit, but I'm not sure.
FC - 9-12 during the superchlorination
CYA - 40-50
The stains are about a year and a half old and are likely embedded in the plaster. I'm uneasy running the chlorine this high for an extended period of time. So the plan right now is to let the FC drop to a more normal level -- but at the high end. My sense is that the stains might lighten up a bit over time, but it may take a very long time. I still remain uncertain whether it's the chlorine or cyanuric acid in the pucks that lighten stains.