As Michel said it sounds like Cyano
. Does it come off in sheets? Usually this stuff covers the surface of your rock or substrate and its a very thin sheet in apperance. Often air gets trapped undeth and causes it to bubble up.
If your tank is still cycling then this will proably start to fade as the amount of nutrients in your tank fade away. The eaiset thing to do is to syphon this out of your system with a small hose when you do water changes or if you have alot do a quick cleaning between water changes.