thanks janet, but that's not the one i was thinking of. that was a spring stain, this one is recurring. i guess i imagined it.

so let's say that it is organic. why/how would it be impossible to brush/scrape up, and why/how would it keep reappearing in the same spot? that's the part i can't wrap my mind around.

and if it's not organic, why/how would it respond to higher levels of FC?

BTW, i have 0 CC, and when i shock the stain goes away but then comes back when the FC gets back to lower levels.