No aggression because you have a tank twice the size, cmor. One tang is not even supposed to be in anything under 75G, let alone two tangs in a 55G. No offense to thread OP, but this is irresponsible fish buying. If you researched a little more, you would know that this is asking for trouble as melosu said. Tangs have very high bioloads compared to other fish, and having two is bad news. Tangs are extremely active swimmers and there is just not enough room for two tangs in a 55G contrary to what anyone else thinks.
And on the off-chance you already knew that tangs can't be in anything under 75G, but went ahead and bought them anyways.. then good luck to you and your fish sir.