Its hair algae. I showed it to the staff at elegant reef and they confirmed. And your right it is easy to come off already when I use a tooth brush. I dont really have to scrub hard. I just thought that doing the 3 days would help maybe kill some more off. If I was going to do a water chabge then I wouldnt have start the 3 days. But since im doing one when this is over I figured it would hurt.