Branching Frogspawn question
 

Had this coral for more than a year and when was having new branches before they would just seem to appear. Last few branches there's been a large bubble forming first, ideas why?
http://i67.photobucket.com/albums/h316/das75/FS.jpg

My frogspawn went through the same thing...but usually when it was stressed. I did a water change and the big bubble went away for me.

Is there any other corals close to the frogspawn? My frogspawn did the same thing when some polyps fell down near it. The bubble was the start of a few long sweeper tentacles.

I've seen people explain that it's a spawning behaviour, too. Not sure myself, though, as I've never experienced it.