I'm been reef keeping close to decade and had strange experience this last week.
My last tank lasted 6 years before losing power while away. I have slowly and carefully restocked tank. I had 4 tangs in system in two different connected tanks.
All fish were quarantined with Copper Citrate and Prazipro for 2 weeks. All ate well and and had not visible scars, parasites, fgungal infactions ect.
I had them in same system for about 10 weeks and 3 of four died