I'm not too savvy on posting pictures but if this thread needs it I'll do my best later.
I've had this home for two years and it has been blessed with a trouble free pool for the last 12-16 months. Water was always clear and levels were acceptable. Then we started seeing a dark blue algae looking infestation on the walls of our pool where there isn't much sunlight hitting it. I can scrape off a bit with my finger, but it's very thin. For all I know it's a stain.
Today I got an algae brush and put some muscle into scraping the sides of the pool with it where this blue algae or stain is. Nothing changed. I'm unsure what it is or where to go from here. Would draining the pool and acid washing the sides fix this?
Thanks in advance.