What is this

[rickysreef]

 

[143MPCo]

aiptasia

 

[ReeferMaddness843]

Looks to be aiptiasia. It's a pest anemone and will sting anything nearby. Don't attempt manual removal as it will release spores into the water column and multiply quickly. Personally used Red Sea Aiptaisia X with great results.

 

[Run4Fun]

I agree with the above. Get it out ASAP and carefully....

 

[cloak]

Being that it's on your substrate, you should be able to scoop it out with a net.

 

[SeahorseKeeper]

Looks to be aiptiasia. It's a pest anemone and will sting anything nearby. Don't attempt manual removal as it will release spores into the water column and multiply quickly. Personally used Red Sea Aiptaisia X with great results.

This is the method I would go with. Any sign of stress and spores will be released.