a little help please

[maryannr]

Can anyone identify this round bluish thing that's growing on my LR? I think it might be some kind of sponge. It's been there for a couple years and hasn't changed. It dosen't seem harmful. This will be my first picture upload so I hope I do it right
Thanks

 

[Sniperhank]

Looks like a sponge to me. That is an amazing looking piece of LR btw.

 

[maryannr]

Thanks. The tank's been set up for close to 5 years