What is this on my gsp?

[Crogling]

Got this yesterday at my lfs. I didn’t notice the brown until I placed it in my tank. Any help is really appreciated

 

[Mr. Mojo Rising]

brown on the gsp? I dont see anything.
Maybe you can draw an arrow to what you are asking about?

 

[Crogling]

It’s partially covered a part of the gsps mat.
I hope this picture helps

 

[shakacuz]

It’s partially covered a part of the gsps mat.
I hope this picture helps

potentially a sponge. hard to tell without getting closer

 

[MERKEY]

I second that it looks like a sponge....you can use a tooth brush to try and scrub it off.

Sponges are harmless until they start doing this.