ok so i have a 55 gallon tank with 4 cichlids, a pleco and a bala shark in it. ive had all 4 cichlids for a long time now and never had any problems until yesterday. i did a half tank water change and noticed last night that 3 of the 4 (the "followers" ) were all just hanging out at the top of the tank and today i noticed that only one of the 4 is still at the top. on closer inspection i saw that most of her tail fin along with her bottom lower fin is half way gone! i watched awhile and all 3 of the other cichlids are picking on her and chase her if she doesn't stay at the very top of the water. anyone know what caused this and how i can fix it? they won't kill her will they? i thought maybe i mixed up their territorial hiding places when i cleaned the tank but im not really sure if thats it?