What is this and how does it happen. I have looked at that FA thread and it doesn't look stringy like those pics. Is it harmful to my fish. It stayed like this for about two days which was how long my aerator was off for, then after some rain it cleared up some.

It's algal, and it's floating from O2 bubbles (hence the disappearance after rain), but that doesn't require it to be FA. Hold on for an expert opinion.

Dr. Perca, you out there?

See this.

http://aquaplant.tamu.edu/database/algae/filamentous_algae.htm

esp. Lyngbya

Thanks for that link. Those pics look more like mine. I saw the management options on the link also but so many to choose from. Any ideas on how to treat this and why it got out of control so fast. Help greatly appreciated.