It's been over three months since i put six angels in a 400L tank. at first they seemed to be fine with each other, they always swim in groups, no one gets left behind etc. now these days i have noticed that they have become really vicious and keep on snapping at each other and chasing each other up and down the tank. i have also noticed that in this group, my two half blacks are the most docile, whilst the two pearlscale zebras, pearlscale gold and pearlscale koi are the ones who fight with everyone else. what can i do to stop this happening? add more angelfish? i'm going to get more fish on thursday! 
