What is Growing om my Zoanthid

[Braveheart!]

start a salt water tank four months ago after being away from the hobby for 20 years. Can anyone tell me what is growing on my Zoanthid. Also is it good or bad. thanks. The Coral with the tentacles

 

[blaxsun]

Aiptasia. Pest (bad) - you don't want to let them get a foothold.

 

[Braveheart!]

Aiptasia. Pest (bad) - you don't want to let them get a foothold.

thanks