I just noticed what looked like two bugs (round backs and yellowish) attached to the side of my pool, about a foot under the surface.
I ground them off with a pumice stone and under them was a black pit about 1/16" deep.
I couldn't get rid of the black.
I've taken good care of the pool for almost two years and haven't had a speck of algae.
These may not have been organisms. They may have been some kind of solidified bubble.
Does anyone have any idea what this may be?