Noticed these on my rock

[16fishes]

I noticed these dandelion looking things on my rock and got scared. I also noticed some hair like stuff next to my favia and on my candy cane. I’m new to the hobby and I’ve only had this tank for about a month. Does anyone know what this is or how I can get rid of it?

 

[sixty_reefer]

Zanclea hydroids, they are a true pain and fairly invasive

 

[castellanamattia]

Are hydroids in my opinion - true pain at that stage. I also have some in my sump, but never saw one in the display.
You could check this out: https://www.reef2reef.com/threads/hydroids-how-do-i-eliminate-they-have-taken-over-my-tank.329188/

Good luck!