What is this

[Snakerdc]

This is growing on a few of my live rocks

 

[Angelfish56]

What fish are in your aquarium

 

[BelleMorte]

I am no expert and still somewhat new but from all I have seen and read on here it looks like it might be a sponge but I could be wrong there are others on here better at this then I ever will be

 

[mr_X]

+1. it's sponge.