What is this

[Leeh24]

Am in the process of upsizing my tank and I was moving some of my filter rock and found this on one of the pieces. Any ideas what it is ? Good or bad ? Lee

 

[Sniperhank]

Yellow sponge. Good guys and harmless. Simple filter feeders.

 

[Leeh24]

So keep it in sump ? Or better in tank ?

 

[Sniperhank]

They are fine where they are and won't hurt anything. They grow under many of my rocks, I forget they are there.