In this video, it looks like the jagged edge on the tail fin that I saw is just its coloration. I can see a few diffuse white spots on its side. Trouble is, that doesn't allow for a positive ID. Given the way it looks, you can rule out velvet. I think you can probably rule out Brooklynella. That leaves either marine ich or flukes. I can't tell you which it is from the video, you'll just need to watch the fish for a few days. If the spots get more numerous quickly, then it is likely ich and you'll need to move the fish and treat with copper. If they stay about the same, then it is more likely flukes and you have the option of treating with prazipro right in the tank.
Jay