The amt og tangs in your tank is way too much..... Heavy bio load and also i dun think its right to squeeze that many fish which need ample of space to swim into a 3 footer.... Naturally a scopas tang being zebrasoma would wack a newcomer purple tang which is a zebrasoma too..... You wun see problems for now but once your tangs get bigger and more established, you willsee war.. suggest you remove a few of them instead of adding more....
My 2cents