Columnaris

[ChileRelleno]

I'd suggest a 75%+ PWC, carbon to remove the Maracyn-2 and then maintaining the 72'f , Pimafix & salt for another week.
Then return the tank's water chemistry & temp to normal and add your quarantined fish.
Columnaris can be a persistent pathogen, watch your new additions closely, and be ready to repeat temp, salt & Pimafix at the slightest sign of a repeat.