Chromis are known to carry uronema. I have never had it myself, so cannot say for sure based on the photo of the clown, but I understand it to be bad news. Plus I do not believe it can be eradicated by going fish less like other parasites. In this case, velvet might be the better option. Maybe snorvich can comment.
Simply underscores, for me at least, the importance of QT. I simply cannot understand why folks play Russian roulette with their tanks - it's just a matter of time, frankly. I've been using a strict QT for over a decade and I both spend less on fish and have a better collection to show for it.