I have two questions about pools.

1. About six to ten inches of mortar are missing from the top corner of an
edge of the tiles at the top of the pool. These tiles get wet but this
particular edge is about two inches above the water line.

What grout (mortar?) is used for edges where horizontal tiles meet vertical
tiles near water?

2. I have green spots that seem to be spreading on the walls of the gunnite
pool, in the deeper areas. The water chemistry, as checked by Leslie's Pool
Supply, seems ok (they said the chlorine is perfect, the pH is perfect, the
Calcium is fine, the total dissolved solids are very low, and the
Phosphates are a tad on the high side.

I assume it's algae (but how would I know)? I shock with three pounds of
chlorine (35,000 gallon pool) about once every two or three weeks.

I've been scrubbing the green growth off but is there an easier way to
identify and then remove whatever it is that is causing green growth in
tiny spots (about the size of a pencil width) on the gunnite walls?