It really is a matter of the light and nutrient balance. I had this algae and after a period I got the light to 7 hours and it balanced the nutrients and that was it, no more black brush algae in more than six years. It can be encouraged by the longer and brighter days in summer, which shows how important the balance is. I had a fish room so thick light-blocking blinds worked for that. But it is all down to the balance. And you should never dump toxic whatever in a fish tank. Use nature to supplement nature.
