Any idea what this is growing out of rock?

[DustinDec]

So we have long hair algae and we’re now running GFO, added a few urchins, reduced feeding, ect. Seeing very slow improvements, but I noticed one dead snail and another seemingly on its way out. Looking at the rock, I noticed some odd transparent thing growing all over. Thoughts?

 

[BristleWormHater]

White sponge. It is harmless and goes away on its own usually.