The stains came before the shock. I shocked thinking it would take care of the stains since the small vitamin C test didn't have any affect. I'll try both the ph down-in-a-sock and trichlor tests, but I have a really dumb question about the puck. I have "stabilized chlorine sticks" (brand and item: Bioguard Stingy Sticks). The active ingredient is trichloro-s-triazinetrione. Is that the same as the trichlor puck you mention?