Kick Ich is not an effective ich treatment. There is absolutely no way to cure ich in a reef tank; although the market is flooded with products that claim to do so. You need a big QT/HT or even Brute containers and treat with Cupramine or Chlooquinine Phosphate (hard to find). Your DT must stay fishless for 12 weeks to wipe out the parasite. Black ich is a minor ailment compared to crypto (marine ich). You're experiencing the inevitable consequences of not quarantining all new fish. Curing ich in a tank like yours is a miserable job, I've done it....but only once. Sure, ich probably killed your vlamingi tang and it is capable of killing any fish. Ich is often taken way too lightly until something like this happens. I'd read the opening posts of the ich stickies above, written by Snorvich; understanding the parasite is vital. FW dips are useless with ich, the parasite is buried too deep.