What is this

[Snakerdc]

His is growing on my live rock

 

[BelleMorte]

Again I am not an expert but from what I have read and seen on this site it looks like a sponge but there are others that can correct me if I am wrong

 

[Biocube14]

It's a moldy green apple.. Lol not sure what that is

 

[Angelfish56]

What fish are in the tank

 

[slitherbomb]

Yeah, probably a sponge. I've got a couple on my lr.

 

[paulace2372]

Yeah I believe it's a sponge, good for your tank.

 

[the_fish_man]

I have a ton on my rocks that look just like that It is just a yellow ball sponge they are filter feeders and are great for your tank.