What is this? Algea?

[Devilutionz]

Just today, I found out that the top of all my rocks, originally clean rock color are now brownish, on the side there was no discoloration, just the top part of all rocks.
What could this be? Could it be some time of algae? If it's algae, how come it's only on top of the rocks
Thanks

A link to a pic

http://www.pixilis.com/?p=file_view&id=53382&id2=&size=large

 

[Nick_kun]

It looks like bacteria, most likely cyano. It will go away when the tank matures some more.

 

[KrazyReef]

Second to that. Normal cycle process. It goes brown before it goes purple !!!

 

[barometer]

looks like a standard diatom bloom to me, which will probably pass on it's own in time if that's the case

 

[Devilutionz]

That's a relief. Thanks guys