Ok, if you want to try the raising the chlorine level route, assuming the stains are organic, which we think they are... I read a post by Waterbear where he told another forum member to raise the Chlorine level to 30ppm and keep it there until the stains are lifted. So you can try to keep raising your chlorine level until you get it to 30ppm and keep it there a couple of days or whatever it takes.

The downside is that if you have metals you may wind up with the metal staining after your organics are gone. If you do we can deal with that by using Ascorbic Acid.