Black spot on Goni

[Selyan]

Hi, looking for help figuring out why my green Goni is unhappy. Tank is 5 months old, parameters are all generally fine, I have 2 other gonis nearby that have been happy for 2 months, while this one is never fully extended and shows those black spot. Any idea what might be wrong?

 

[Gumbies R Us]

@VintageReefer

 

[VintageReefer]

Most likely a dead spot or stressed spot where the polyps are retracted and algae has grown on the skeleton. Algae will prevent the polyps from coming out and can spread and cause more damage.

 

[Selyan]

Is there a treatment I can do to stop further growth of the algae?