I'm overdue for an update so here goes. The tangs finally cleared QT after over a month in a bare bottom tank with a very mild dose of CP. They did great in the QT together, but soon after introduction to the main tank they became pretty aggressive with each other.
Two days later they got ICH, and I observed its progression for that day. I ended up blocking off the end of the tank with cardboard in order to net them, and back to the QT they went. After a 25% water change I dosed the QT with CP again (1/8 tsp per 40g) and the next day I did another identical dose (by this time almost all of them had ICH). Two days later I did a 5g water change and dosed another 1/8th tsp... The following day they all started to clear up and they continued to eat well... All looked great as no ICH returned in the following days. Roughly 4 days after the ICH cleared one fish appeared to shed its slime coat... This alerted me to a possible overdose of CP in the system... I started water changes, but they ended up dropping like flies. Sadly none survived...
Here's a video of them after I introduced them into the CF Tank...
[video]https://youtu.be/ReV8oKcAvyw[/video]