I have a 240 gallon tank with three fish in it, two convict tangs and one cherub pigmy angel. I've had all three for probably seven years. I would like to add more livestock but, I fear that any new fish I introduced would be terrorized by the three fish I currently have since they've pretty much established their territory which is probably the entire tank. Not sure what to do. I could try catching the three and taking them to my LFS and starting afresh which means I'd probably have to dismantle my aquascape to catch them. I tried a few years ago introducing three pigmy angels by placing them in small clear plastic containers and putting them in the tank so that my cherub angel could get used to them. The cherub was very curious at first but after a week he seemed to lose interest. So, I released the three angels into the tank and it didn't end well. What would you suggest?