Did they pass away in QT? Copper can suppress brook and velvet buy not eradicate. So if you were running correct copper levels they should've remained alive for the time being. Unless they were too far infected to begin with succumbed to stress meds or parasites. Sorry this happened. What copper product did you use. What level was your copper and what kit were you using to test copper levels?All the fish died I think it was brook I had no viable way to treat them. Kick ick didn't work or copper treatment. I've been preemptive at this point and purchased formalin so if it happens again in ready for a curative treatment for external parasites. Waited 75 days for the lifecycle to end.