i have recently started to use a acclimation chamber to introduce new fish into the tank. it works well. however you want to introduce multiple fish. if your tank can handle it and all the fish are about the same size then i would add them all together. it would make it hard for the existing fish to pick on one in particular. they would be overwhelmed because of the amount of new fish. if it was my tank -emphasis on MY- i would do a large water change, feed the fish well turn the lights down to dim and ad the new fish, leave the lights down low for a couple days. you want enough light for the fish to find hidy holes but not spot each other across the tank. if your egzisting fish have definet territories you should try to break them up as well. that will really help. then gradually raise the lights back up over a couple of days. good luck