How long would you let 2 tangs fight for?

[corpusse]

I just lost my Chevron tang of 7+ years but "replaced" him with a Naso. They were originally going in together in my 180. I had him in QT since black friday. The other tang I have is a smaller Achilles. The Chevron would beat him up a bit and then he'd fight back but they more or less accepted each other. I figured although 3 in the 180 would be a little cramped it would allow them to split up the aggression instead of just the one on one madness that's going on now.

The Achilles is a lot smaller then the Naso but he's circling him like a shark and tearing up his fins pretty bad. The Naso for his part is just taking it and when it gets to be too much he'll spike him once to shoe him but won't chase him down. The Naso did manage to eat a little bit of Nori this morning between fights. I know there is the possibility in the few days the Achilles was the only tang in the tank he claimed the whole thing as his and will no longer tolerate new tangs. I'm just wondering how long I should let them go at it. I didn't drain the QT just in case the Naso has to go back in. Obviously I have been keeping tangs a long time, but the Achilles I've only had since March and never introduced him to a new larger fish he was the last big addition and the reason for the 180 tank.

Also I do know the Naso will outgrow the 180. I will upgrade tanks before he gets massive.