This started about five days ago...I have 11 redtail sharks in a 55 gallon tank and they are not killing each other..They hang out together at night and stay at the same spot in the corner together..They sometimes quarrel but not to the point of stress...I have read in the internet, that a person should have only one redtail shark to a tank or more than six redtail sharks in a tank to calm the aggression..So far, day 5, things are looking okay where I dont have to take any of my redtails back to the LFS..