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
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