Too bad on the stock issue, IMO, the best black algae control tends to be a good group of algae eating fish. Siamese Algae eaters are good at keeping
this type of algae under control, and Rosy barbs are also known to snack on this type of algae.
In your case, it is best to manually remove any affected leaves, plants and remove - if possible - any decor and clean it. It is nearly impossible to remove black algae without tearing up the plant leaf and causing tissue damage so simply snipping off the affected leaves is the best way.
Good Luck !!
