You risking the life of these fishes by not doing a proper cycle. Twelve tangs in a two weeks old tank? This ain't packing sardines in a tin where we filled it up to the brim. I'm sure you didn't know about how fast tangs can grow. You need more open space for swimming and much more caves for so many tangs. Yes you can keep them alive but they are not healthy, just alive. Definitely shortening their lifespan. Of course you can always buy a new replacement for the dead fish and claim that you are very successful and no one would know about it.
