When my tank was first setup I had brown algae growing like your rocks look like and lots of airbubbles as it turned out coming from it. I just did small water changes and added my clean up crew including a few emerald crabs and about a week later no algae and no strange bubbles not rising just setting there. It wasn't bubble algae either.
Im on my way to the lfs now to see about a cuc.....i just did a water 8 gallon water change yesterday