What symptom did my clowns have?

[George]

At first glance I thought you fish had lymphocystis (lympho) because of large cotton-like growth on their bodies. After I watched the video a few times, I did see some small white dots. Maybe they have both lympho and marine ich. Unfortunately diagnosis a fish disease is very hard over the 'net with photos and videos. Best to look under a microscope.
With that being said, if they were my fish, I would put all fish (not only the clowns) in a quarantine tank and treat them.
I understand not all people want to do that. If you decide to leave them in the tank, make sure your water parameter is good. Feed them high quality food (high protein food), and feed them often. I noticed one of your clowns is on the skinny side.
BTW, not sure where you heard about using melafix. Melafix is advertised as an antibacterial (even that's a stretch). Neither lympho nor marine ich is a type of bacterial.
Good luck!