I have a 10 gallon tank that has two angelfish. (there are several other kinds of fish as well) When we bought them we were told that they would all do well together, and they have, for the past 2-3 months. I changed the water on Sunday and decided to rearrange the plants and reef. Apparently this was the wrong thing to do. The smaller of the angelfish has begun to attack the bigger one! When someone suggested that I move the stuff around I immediately clued in that maybe I had moved the stuff TOO much so I moved it all back to the original configuration. The pecking continued but now seems to have slowed, if not stopped...at least towards the injured angelfish. He has almost no tail (I say he but have no idea) and the front fins are obliterated. I feel horrible! I've added antibiotics to the tank in the hopes that he'll make it but the aggressive fish still seems to be "charging" at the other fish in the tank. What am I doing wrong??? The PH seems fine and the temp is also OK. Any suggestions would be greatly appreciated. Thanks!