Previously, my pool had quite some yellow algae. The water was very cloudy.
I shocked it twice, and have been maintaining chemicals at the correct level. (FC 2~3, CYA 20, PH 7.5).
Now the water is crystal. The algae are dead (no CC at all). However, there are still some black dead algae at the bottom and wall of the pool as in the attached picture.
I tried to remove it with brush, but it didn't work.
What can I do? Should I just wait for more time so that they disappear automatically?