DO NOT STIR UP THE SANDBED. (Yes I am yelling) The air pockets are naturally occurring in DSB's (someone else chime in here, are they Sulfur Dioxide??) and are part of the filtering processes.
Pretty sure what your seeing is Nitrogen Gas. (Nitrogen Cycle). This is good. I'd probably not disturb the bubbles... Just let em' be. Happy Reefkeeping!
Don't worry about the bubbles, Yes they are part of the denitrification process and this means that it is starting to work! The Nitrogen bubbles are the end product from the anaerobic bacteria breaking down the nitrates in the tank.
JJ
Bubbles in the sand bed are not a bad thing at all. I'd be curious though if anyone has actually tested the gas bubbles that we see (not sure how that would be done), because it may be just co2 from any of the usual algae that grow in between the glass and sand. Either way, no prob!
I would think that if the pockets were sulphur dioxide, you would also see the typical black bands around the pockets. The bubbles are probably trapped air from the initial install or nitrogen from the denitrification process.