Please Help

As a followup to my previous post, thinking it was possibly PH shock, I
put a couple of my mollies in the new tank (since they like alkaline
water and are used to my water and they turned whitish and started to
die within an hour. Everything in the tank is new. Any thoughts? An
artifical plant, the air bubbler, the gravel? I am very bummed out and
baffled. Some sort of toxic thing, I would think, since I know of no
disease that works that fast.