I have read that it is not as likely on a vinyl surface but I think this is black algae. I brush it off and it reappears in the same spots a couple of days later. Water remains clear. Is any algaecide recommended or just more chlorine and brushing?
FC 7
CC 0
PH 7.6
CYA 60
FC 7
CC 0
PH 7.6
CYA 60