FML Dying fish

[MarkoD]

bought a blonde naso tang about a month and half ago from a store that said the fish was eating.

brought it home, it wasnt eating, i tried every known food for this fish and all it would eat was nori.

i had it in quarantine for 3 weeks and moved it into my display.

its been in my quarantine for about a month now and couple days ago it got ich. (but it was still eating)

i get home today, the fish is stuck to a powerhead but still alive.

i quickly get my quarantine going and put him in there. he's floating around but doesnt have much energy to swim.


seriously what made this fish sick 7 weeks after buying it? none of my other fish are sick or showing any signs of ich. they all eat like crazy.