Purple may be cyno bacteria. dose it blow off the area easily? If so that would be my guess. So with hair algae and cyno you have a water problem, Excess nutrients would be a start, lack of water movement and wrong lighting spectrum all are factors with cyno and hair algae. IMO
Air bubbles is not uncommon when dealing with cyno. Not sure what causes them but when I had cyno I had all kinds of bubbles trapped in the cyno.
How old is the tank...... Your using tap water?