In my 18 gallon tank I have had 2 cory catfish, 1 barb, and 2 zebra danios. Yesterday we added an Australian Rainbowfish (nearly same size as barb), and from moment one the barb attacked. We have 1 barb because our other one died a couple months ago and we never replaced him. So this one has been king in the tank for some time. Anyway, we noticed the rainbowfish acting a little lethargic last night, and since we dont have a quarantine we seperated him from the barb by putting him in a large bag full of the aquarium water with a small air hose to give him aeration. This morning I can see that his fins are shredded and his eyes have some whitish stuff on them (see photo). I dont know if its from damage or disease. We really dont know what to do, Im afraid of the barb picking on him to death (literally), or we are faced with taking him back. Will this barb ever allow anyone else in the tank? We had 2 platys for a little bit and he didnt bother them, and he rarely cares about the others as well. I dont know whats different about this new one. He's a meanie!