fighting tangs

i just put 2 tangs in my tank, and they are kind of fighting, not stabbing or bitting just chasing really, but how long should i let them do this? i know its natural but i couldnt find any where that says a time limit if they don't stop?

Received a Yellow Tang from Saltwater.com, acclimated for a few hours, then dropped him in......Instantly my Powder blue Tang started attacking it. the yellow is alot bigger than the powder blue. Question...What can i do.??...ive read that people have the same problems, sometimes they go...