NEED HELP STAT!

Hello Everyone!! I hope y'all are having a good Monday!! I noticed some white stuff on several of my fish this morning. I have attached some pictures of one of my fish, a yellowtail damselfish. I have been so busy with work I haven't been able to spend as much time with the fish as I usually do so I don't know when the white stuff started to appear on him.

I also have a yellow tang, starkii damsel, eyelash blenny, clarkii clown, oscellaris clowns (2), false lemonpeel angelfish, ...