I have these weird grey spots which formed on the side wall of the pool (my pool is very light blue so I can easily see them). one is 1/1.5 inch big, the other are small , more like dots. I tried to brush them off but they don't go away. I just came back from 2 weeks vacation and have now some at the bottom of the pool.Any idea what it can be?
here are my chem info. I boosted my SWG while away just to make sure I will not get a bad surprise upon my return.
CYA 40 (that just dropped while away, I will readjust to 70)