[WorkinMan]

Do you have a sump? The little bubbles, or micro bubbles, are why many people have baffels between the overflow and the return sections of their sumps. They help prevent microbubbles from finding their way into the display. They are cuased by the fast moving water from the overflow mixing with air when it hits the surface of the water in sump. There are other cuases as well, but this is one of the main ones. I'm having the same problem with my set up right now and am working out different preventative measures. I don't think they are in issue with a FO set up, but once you start getting into corals the microbubbles will collect under some types of corals and form small air pockets causing problems for the corals.