We have a 55 gal tank. Pretty much fish only. One regal blue tang, a yellow tang, one true perc, a foxface and a featherduster for fun. Went to the store and got a sailfin tang and coral banded shrimp and two firefish. Was a bit worried that the mamma yellow tang would pick on the new sailfin. Yellow did little chasing around just to let the sailfin know it is HER tank. But what freaked me out was the perc went nuts on the two firefish. I couldn't catch the perc or firefish to get them out (and do what with them?). The mean ol perc basically murdered the two firefish. Who knew?