I would not just add One Your best bet is to add 2 more, when i originally added my fire fish i added 2 and they where fighting like crazy, after that i added 3 more, One jumped out and then they where fine for a wile and actually kinda paired off, 2 on one side of the tank and 2 on the other. Then Freken Coral banded shrimp decided to make dinner out of one so now i have one pair on one side and a loaner on the other. If the other one come to there side they kick him out.