Small stains

[Mesamav]

Hey guys,
I have my pool sparkling so far this year but last year before I found this site I had trouble with things. I had what I think is black algae and a few other things.
I still have some very small dark spots on my plaster. Anything I can do to get those out?

 

[RobbieH]

Try rubbing a trichlor tablet on them and see what that does.