Sick Butterfly, please help !!

[FWC]

So I got a longnose butterfly a few weeks back, looked all good outside of a spot on the side of her head, I figured it was ick so whatever.

Fast forwards a week or two, butterfly gets sick and looks like it has ick. No big deal, fish is still perky and eating, it'll go away.

Fast forwards to last night, fish is all good, still perky and eating, and has been looking better on and off for the past couple of weeks, almost 100% clear looking last night.

Skip to now, and fish is bad. Still swimming, but only in its favorite corner and not around the main tank. Also wont eat. Covered with something. Tips of fins has brownish "Stuff" on them.

Leopard Wrasse and Percula Clown are both fine.

How do I fix it ??

Also ignore the algae on the glass, I've been a bit lax with tank scrubbing as of late.

Also sorry if some of the pictures are blurry, I'm not in the mood to sort through them.