I’ve had wrasse problems as well. I recently quarantined an Exquisite, Pintail, and Melanurus. All were feeding and like 3 days in, the Exquisite dropped dead. The Pintail started getting lethargic and stopped eating. This all started happening before I medicated. I started GC, and the Pintail got more and more lethargic and died. I got worried so started ramping up copper during the second round of GC, figuring I had nothing to lose and that I would probably lose the Melanurus. To my surprise, the Melanurus made it through quarantine well and is now in my display.
About a month later (about two weeks ago), I tried again with a Pintail and Exquisite. Again, both fed the first few days though the Exquisite ate more aggressively. After that, the Exquisite became lethargic and wouldn’t eat. I started GC and like the Pintail before, the Exquisite got more and more lethargic and died. However this time, the Pintail is doing fine and has progressively gotten more aggressive toward food and is even becoming a lot less reclusive.
What is odd is that the fish start out eating and then take a turn for the worse a few days in before I start medicating. It is also odd that something can attack and kill these fish so quickly, but it doesn’t kill them all or even cause them all to show symptoms.