It's a reef tank. You are going to have all kinds of stuff growing and out competing each other over time.
All tanks go through the 'uglies', until the dominant algae (usually coralline in a perfect world) takes over. I would not worry about nor do anything about it, unless it becomes an issue. The natural reaction is to remediate it, but the tanks ecosystem is probably way ahead of you, and whatever critter eats the newly arrived algae, that will be the critter that you notice come on the scene next (assuming you are adding frags and stuff to the tank).
Dennis