Bought 5 silver dollars about a week ago in a new 60 gallon tank. (Tank was fully cycled before they came in ) Anyway they were there over a week and doing well. Added 6 black skirted tetra last night. All was well with the two groups schooling together before bed. This morning we woke up to 3 of the black tetra alive and with fins nipped. We then noticed the silver dollars banding together attacking one of the remaining skirted to death. I managed to get the last two into my shrimp tank. ( survived an emergency dump directly in other water conditions for 8 hours now. ) We were going to add Angel fish but are now scared. Anyone heard of this? We kept the silver dollars well fed and have many hiding places. Had anyone else had problems. We always heard they were non aggressive. Please help.