Bubbles forming in sand

[Endler's Game]

So my tanks been running a few months, and in the last couple of days, I've noticed some weird gas bubbles forming in the sand against the front glass. The sand is also turning a little brown there. Anyone know what this is and if it's a problem? Here's a pic:

[seabass]

Looks pretty normal to me. The brown algae is actually just on the glass (because it's exposed to light), and not through the entire bed; sometime you will see different colors up against the glass from Cyano (which is also OK). The bubbles could be from nitrogen gas, or just fauna that lives and burrows in the bed. Nothing to worry about.