What is it?

[Dewandaru]

what biota is this? type of pest or not? reef safe or not? Thanks

 

[ISpeakForTheSeas]

what biota is this? type of pest or not? reef safe or not? Thanks

Welcome to Reef2Reef!

Those are colonial tunicates - some species can be incredibly invasive (to the point of growing over live corals), but others are totally harmless.

If possible, I would isolate them so they don't spread too much, but you should be able to just scrape them off/remove them if you don't want them.