hello and welcome. :bounce:
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you should not need the formalin, how ever i would recommend de worming them all.
I would de worm the upset "hissy fit" discus separately.
raise the temp to 32 degrees (your albino cory will not like that one tiny bit) slowly.
melafix will not help in this situation and the same goes for the epsom salts.
since you have metro use that, you will find a lot of posts about the dosing ratios.