Is this some type of sponge?

[oldedb]

Just noticed this in a shady area of my rock work. Tough to tell in the pictures but it has a white/yellow look to it. It is very porous with pin size holes but then it has 2 holes that look like they are the size of a nail.

Any reason for concern?

Sorry for the crappy pics... haven't figured out how to take good pictures of the tank yet.
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[1mbrews8]

looks like a sponge ) but I'm not 100% sure

 

[jennm]

Yes. Perfectly harmless.

 

[nickg]

yep what she said...