I am not a pro but FWIW It sounds like an infection and you may lose them all. They should be over any acclimation issues by now, IMHO I would throw some antibiotic soaked pellets and hope the problem is a bacterial infection. The antibiotics will not help if you have a viral infection. I am not sure there is anything you can do if it is viral.

I would also find a new source for the future.

Just my 2 cents

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