Its a part of starting a new tank. Try to reduce excess nutrients - feed once every other day, and if you feed frozen food, thaw it out in RODI water as frozen food tends to contain phosphates and these are a fuel for nuisance algae. Minimise lighting where possible and suck as much out with your vac, when you do you PWC.
It will eventually go away, and if you have coraline algae on your rocks - this will eventually take over. It's all a part of the new tank cycle.