I've had it like that on my rocks before. Just gave it time and it cleaned itself up pretty much, with the help of a CUC and myself.
One thing i noticed was that i might have silicates in my tap water, causing some brown algae. So i got some Phosphate Sponge and tried lowering my Phosphates/Silicates. Seemed to help a little bit. But this was after i gave my CUC a chance at the job.