To determine if they are in fact air bubbles or some kind of residue in the water, take a sample of your tank water out in a glass and let it stand for a few hours. If they are air bubbles the water will clear up, if they are particles, they will sink to the bottom of the glass.
I remember a few threads about the same issue where the air bubbles were caused by a faulty, or wrongly re-assembled filter.
There is still the possibility that you are dealing with a bacterial bloom. It usually will resolve on its own, but keep an eye on your fish's breathing, I have read somewhere that these bacteria compete with the fish for the oxygen in the water!