What is this, looks like a sponge

[ChamorroSD]

 

[Flippers4pups]

Yep, you are correct!

 

[ChamorroSD]

Thanks hopefully is not harmful

 

[Katrina71]

It's pretty. I'd keep it.

 

[Tautog]

Sponges are fine. Keep it

 

[TheZachariah]

Ive had one in my tank for about a year and its done no harm Just filters water, grows, and makes me wonder if its a tunicate from time to time with the tube like branches it has (its a sponge)

 

[Arringar]

Sponges are a good sign of a healthy tank and are useful to further improve water quality.

 

[ahiggins]

love these guys, I have one in my overflow about the size of a half dollar bill and one on the underside of an rock ledge.