Rocks in tank

[moetec]

i have 3 rocks in my tank and there is brown stuff growing on them now. any idea what it is? help please.

 

[mattrox]

My guess is algae. Any pics?

 

[blkhrt]

Its common, just either flip the rocks every week or just scrub them. Ensure you are changing the water, this will help as well.

 

[Wy Renegade]

If its a blackish brown layer that clings to the rocks and scrubs off hard, it is most likely diatoms.

 

[BigJim]

+1 for brown algae (diatoms). They're common in new tanks and they usually burn out after a few weeks.