So what is this?

[Armando]

Are their any Tangs in this tank? If it is red macro usually it is mowed down in a second.

That's a very good question.

I have a Purple Tang and a Red Sea Sailfin Tang in this tank. (They are juvenile though). They both ignore this growth, so this makes me think it may not be algae.

squishy jelly baloon.

this is a good description on what i have as well

 

[~Flighty~]

Tis sounds odd, but can you break a piece off and smell it. Macro smells like seaweed and corals smell, well you know how they smell, a sponge probably wouldn't have much oder if it is healthy.