What is this irritating zoanthids?

[vadryn]

I have this small filament like tree shape thing irritating a group of zoas. Want to ID so I can deal with it while it’s isolated in one spot, if I need to. Pest or don’t worry about it?

 

[ISpeakForTheSeas]

Those are branching colonial hydroids - they'd be considered pests.

 

[Cthulukelele]

Depending on how much they like your tank they'll either die out on their own in the next few weeks, stay right there and never expand, or absolutely explode. Colonial hydroids are a true craps shoot when it comes to how invasive they are