Damsel is not looking too good.

[anhsirk]

Black on one side and labored breathing. I think it’s a parasite. could not find what it is online. Please help.

 

[Crabs McJones]

Hard to tell from the picture. How long have you had him and what are his tank mates? Also what are your water parameters and how long has the tank been running? Do you quarantine fish before adding them to the system?

 

[RichtheReefer21]

Hard to tell from the picture. How long have you had him and what are his tank mates? Also what are your water parameters and how long has the tank been running? Do you quarantine fish before adding them to the system?

This should be sticky in this forum.. like "Before you post, read this"

Would definitely expedite the helping process considering how short time is in some of these disease/parasite threads before its too late to save them.

 

[Humblefish]

Looks like a bacterial infection: https://www.reef2reef.com/threads/bacterial-infections.191511/