I'm sorry to hear about the sick glass fish...
It's really hard to say what it could be, since they're new from the shop, and in a cycling tank - all dye jobs aside, they're probably under a lot of stress right now.
You mentioned white spots - do you think it's ich? Is that what you dosed the main tank for?
(I got lost somewhere, I'm sorry!)
I don't know what to tell you, except to keep the water clean for them. . . I hope everyone comes through okay. . . T.T