it all comes down to the temperment of your flower horn, eg: when mine was around 3-3.5inch he was in a 180gallon tank attacking my aro which is hitting 21inch. they were fighting so bad i moved him into his own 100 gallon with 3 other flowerhorns, 2 severums, 3 synspilums all ranging from 2-5inch and he has systematically killed every single fish and now his on his lonesome and he seems much happier. now i just run a single internal pump and a wavemaker and he seems more then content riding the waves and eating as much as he possibly can.... all comes down to temperment and my dude doesnt share