Assuming sensible choices, the most important thing in successfully adding another tang to an established population is to make sure the new fish is as prepared as possible to withstand a few days of 'hazing'. Asking a just-bought, journey-starved fish to survive this is asking a lot. Do yourself and the fish a favor with a couple of months of QT to get it settled and fattened up. I've added, sequentially to my 265 with resident yellow and regal/hippo, a Purple, an Achilles, a Desjardini Sailfin and just this week a Chevron. The sailfin was bigger, but all the others were smaller. Some initial aggression, but all have survived. My only loss was a Naso that got chased and pinned onto my vortech.