Its the photosynthesis part of the day/night cycle that causes the red cyano or slime algae to manufacture the bubbles. The oxygen bubbles start out small and then get larger and larger before they break off and float away. I wouldn't really worry about it in the fuge. A couple of things happen with algaes and you will have growth of different ones at different times of the year. There is no way to beat those cycles, only to control them with things that eat it. Microblue leg hermits will eat it.