Yes, hydrogen peroxide that you buy in the wound treatment section of stores. As the previous posters said, turn off your filter for about 15 minutes. It will not hurt you BB or fish if you just do one syringe full a day. Usually it just takes one dose to kill off the algae. I have done two syringe fulls in one day in my 29 gallon tank with no problems though. By the next day you should see the algae turning brown or white. That means it is dying.