Turned over a rock and found this.

[sherim37]

Anyone know what these are? They were all over one of the rocks in our tank.

 

[JonsNano]

Possibly pineapple sponges

 

[JTP424]

Try to take a photo in white light, but they definitely look like pineapples sponges, harmless filter feeders, they should eventually go away.

 

[Cthulukelele]

They're Def pineapple sponges. White light would be nice, but shape and location are a dead giveaway

 

[lil sumpin]

Cool find! Welcome to R2R

 

[sherim37]

Does this help