ID Needed

[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

 

[JohnL]

Looks like Aiptasia to me.

 

[Misled]

Looks like Aiptasia to me.

Me too.

 

[Reefing102]

Agreed. Definitely looks like Aiptasia. Most people generally view them as a bad thing due to how invasive they can be (usually spreading very quickly). It seems a popular method to get rid of them is to inject with calc paste or boiling water.