The bubbles are from anerobic bacteria they strip the oxygen from nitrates and convert it to nitrogen gas. The bubbles will make there way through the sand and escape from the tank.
I would not disturb the sand bed at this point as you could cause a crash. Best thing to do is add some sand stirring snails (nassarius) or other sand sifters they will stir the sand slowly letting the tank adjust to the changes.
Feed a little less and/or increase your PWC
's to help with the Cyano
Most people create their own problems by not following the basics and refusing to stock appropriate to their system. Gregcoyote 2013
SPS = Stability Promotes Success