I could be wrong but I feel that may be velvet, especially swimming at the surface like that, it's horrible and a horrible feeling, honestly it's easier to just QT everything, feeling ya pain and sorry for your loss honestly I went through all this and I can't stress enough, QT don't take the risk because when it bites it bites hard and it's actually not that hard, just got to be patient @Jay Hemdal and @Humblefish have some good info for disease and QT. I personally like copper sulphate myself and its super easy, copper hanna checker will make your life easier as well
Happy reefing and good luck moving forward
Happy reefing and good luck moving forward