White sponge like thing

[Garen]

Hi I've just noticed this on back of coral frag. Coral has moved to front of frag which made me notice. Any ideas?

 

[JGT]

Sponge.

 

[Garen]

Is it ok or should I remove it? It looks pretty big compared 2 any others I've ever had

 

[Just John]

If that is a new frag, take it out of the tank and gently remove that single bubble algae. If it pops in the tank it's going to be a huge pain because they will grow everywhere and are difficult to get rid of.