Black Beard is actually a form of bacteria and will inhibit the growth of healthy plants. It also detracts from the appearance of the aquatic environment.
For the removal of Black Beard growth on aquarium plants.
Directions
After a 30% water change use at a rate of 5 mls per 50 litres or 1 drop per litre. (10 drops = 1 ml, 1 capful = 5 ml)
Then daily dose at 1 ml to 40 litres daily or 1 drop per 4 litres
Black Beard growth should turn pinkish red and die back.