What could this be?

[Johnny E]

What is this? It is starting to spreading all over my rocks. Thanks

 

[BONESTOCK]

What the bubble algea? Don't pop them....they aren't good.

 

[steve-s]

Don't think you will find that is valonia. Looks more like a type of compound tunicate or possible bulbous coralline.

Cheers
Steve

 

[Bang Guy]

I've heard it called Red Bubble Algae. The only thing I've seen eat them is a Rabbitfish. They seem to grow slower than Valonia but can still take over a tank if left alone.