I introduced 3 zebrasoma’s -gem, yellow and purple- (the 3 amigos) at the same time. The yellow and gem were a little larger than the purple and it all went well. Unfortunately, unrelated to introduction, after being in tank for some time somehow a bacteria got into the tank and killed some valuable fish including the purple and Gem. Now that everything is cleared up, I’m going to be introducing a purple and Gem smaller than the established YT in the tank. Fingers crossed.