I have several dark patches on the bottom of the deep end of my in-ground pool. I noticed them last year, and they were still there this spring.
I am meticulous about proper levels and cleaning. However last year, while on vacation, the chlorine level dropped to 0 for a few days.
I have brushed and shocked (to 20). I tried rubbing a chlorine puck on the stains, with no effect at all. I treated with polyquat a few days ago. Could these be stains instead of algae growth?
Thanks for any help!
Levels and info:
Pump on 14 hours a day since May 15