It depend of if its velvet or ich. If its velvet, it can kill very fast. If its ich, it can kill fast too depending on the level of infestation. Ich also can dissapear for a few days, weeks and come back twofold.
I'm not sure about this, but based on you posts you may have velvet in you tank. I did not see anything about this in your posts until today. How long has this been developing? Velvet has a fast onset.
Either way I would move fast. Not eating is not a good sign.
Do you know how to fw
dip? It could give you fish some relief when moving them to the qt
If I could beat it, so can you.