I have a yellow, hippo, powder brown, and tomini in my 180. The powder brown beat the crap out of the tomin for about 15 minutes straight but now they are the best of friends. When I put the powder brown in, the yellow opened up a can on him for about 10 minutes, as well. My rule is if the fish can't hide and be left alone after an hour, then it's not gonna work. I only had to remove one fish from my tank using that rule so far. It was a yellow getting whooped by a scopas. That's when I learned that same body shapes equal critical beat down...