what are these

[nathancaspi]

any idea what this is on my rock and if it’s good or bad they look fuzzy

 

[WheatToast]

Those are Pineapple sponges. They are harmless filter-feeders (feeding on phytoplankton and bacteria, though I have never had to supplement these to keep these sponges alive) and should never be removed from the water as this traps air bubbles within their cavities, killing them.

 

[Isopod80]

+1 Very common in new tanks. You may see them spread for awhile but most die back once the tank settles in.