What do you do if you have clusters of black dots on the surface and bottom of your swimming pool?

I have the same problem, my pool shop suggested getting the acid level to normal (around pH 6-6.5) ensuring stabiliser levels were normal and adding granulated chlorine, I added the choline and it went cloudy (don't add liquid chlorine at this stage) leave it for a week then go back to normal chlorine dosing, the combination of these steps should remove the black spot, mine went to a lighter shade of green but is still there, I may have to repeat the first 2 steps as my pool was out of balance.

Did you try anything else that may have worked?

Ian