I would buy a much smaller one and let the one already dominant in the tank stay that way, I purchased both my yellow stripes from the same source two years apart, when I ordered the second I was very specific that I wanted a juvenile as they have no defined sex at that stage, I took precautions in the pairing, I pulled the established fish out of the tank and set her on a 5g tank, I divided the tank with eggcrate to allow the little one to scape if needed, I added both fish to the tank at the same time and she embraced him immediately, I expected some type of aggression but none was shown as she was clearly dominant
this were them just minutes after adding to the same 5g tank
hours later and after no sign of aggressiveness I added the anemone, she allowed him into the anemone without an issue
next day they went back into the main display and been living happily ever after.... get the juvenile!
