If you add another one they will very quickly either pair up or fight to one or both's death.
Maroons are super fiesty clowns, pairing them up can be scary to say the least, but it can be done. If you decide to try, you'll need to get a tiny one for the new one, like .75" . That way they are very different in size so the dominance gets worked out fast, otherwise they will beat each other to death.
I paired mine up about 5 yrs ago and they are still doing fine, but that was one very disturbing night. It's hard watching a 2.5" girl thrashing a little .75" baby, but by morning they were happily hanging out together in the anemone.