What did you shock for? Did you try to rub a trichlor puck on the stain? You can also put some ph down in a sock and rub it on the stain. If the stain comes off with the ph down, then it is probably metals, if it comes off with chlorine then it is organic. You may not have had enough of the vitamin c to make a difference. Did the stains come before the the shock? You wouldn't get any metal stains from low chlorine and low ph, that is why I would guess that if the stains cam e before the shock, the stains would be organic. Let us know if either the ph down or the chlorine work.