my pool is a 20000 gunite inground
my plaster job needs too be redone
every place that the plaster cracks off
and it's down to the bare cement I notice
some black substance almost like algea. when i
brush it goes away or get alot lighter and i can
almost see some green algea getting dispearceing in
the water, but other than the spots without plaster, the pool
and the water are fine, any thoughts to get rid of the stuff

ph 7.3
ta 100
cl 3ppm
cya 40