[HighlandReefer]

The air bubbles are most likely the result of micro-organisms like algae growing on your rock. As these organisms photosynthesize to acquire nutrients they release oxygen which is what you see. If it is a pest algae then scrubbing your rock would be best to keep it from growing and becoming a nuisance to allow coralline algae to grow instead. You will want to keep your nitrate and phosphate readings at zero. Cleaning your sandbed weekly will reduce nutrients trapped in it & prevent it from becoming a nitrate & phosphate factory.