Mroll; I'm really glad to see your FC is still 4ppm and your CC is back to 0ppm - good news.
I'm also really glad to hear you've identified the black spots - I was a little worried it might be something growing and that's why I asked about brushing. Yep, a pool brush is a good tool to have and use, it physically breaks up colonies / biofilms so the chlorine can get to 'em. I think it was Waterbear who compared brushing your pool to brushing your teeth - has to be done to stay clean.

aylad; while I usually wouldn't advise messing with pH that's between 7.0 and 8.0, I've asked mroll to move the pH to near 7.5 to provide a cushion for the upcoming vacation with minimal poolcare provided by sons.