What is a good number of angels to keep in a tank? Do they need to be in pairs? I had added four to my tank about a month ago. One died early on and I have left it at 3 since. I notice that they stick together about 80% of the time but two of the seem to have paired off and sometimes get slightly snipy with the other. Nothing serious but just kind of keeping him in his place. Should I add another or more? This is a 210G tank so I have the room.