Almost all of the time, not always, if a fish has something, it will show within two months in QT. It was in a 45g with a Lionfish. IMO
, that should have stressed it more than being put into a 240g.
I understand Ich pretty well and have given advice on it many, many times in the Sick Fish section here. I've also dealt with it in prior tanks. This acted nothing like anything I have seen or read about Ich. Ich should not come and go like this did. Ich should not also have white fluffy specs. Ich, if it is going to kill a fish, should cause some degree of stress to a fish (loss of appetite, rapid breathing, etc).
Bottom line, it ends up a mystery unless my Chromis end up with Ich. Either way, they will be treated with hypo and the tank will go fallow. That will hopefully clear things up moving forward.