Purple tang got strange white spot during 3 weeks copper quarantine.

[Reef-Tank]

Hello, anyone have an idea what this is white spot on the purple tang top dorsal fin ? He had been 3 weeks quarantine with coppersafe and now showing sign of this white spot. What could i do and how to treat this? This fish got 1 week left for final copper quarantine. Thanks

 

[CivicS14]

Is the white spot like a little cotton ball?

could be this https://www.reef2reef.com/threads/lymphocystis.257461/

 

[Reef-Tank]

Thanks for replying. it doesn't look like cotton ball. it looking like a white paint dot on the top.