What is this??

[Zydan777]

Saw this on the side of one of my rocks. It looks like it has a mouth

 

[DWPhilli]

Pineapple sponge

 

[Auquanut]

Yep. Pineapple sponge. You'll probably see more of them as your tank matures, and at some point they seem to diminish. Nothing to worry about.

 

[Zydan777]

So does that means my tank is doing well?

 

[Idoc]

So does that means my tank is doing well?

Yes, usually a good sign.