Hi, my male betta is in a 12 gallon eclpise. Everything has cycled, so i decided to add 3 small Panda cories, well i acclimated them and about a week later, i was looking at them, and one of them had his tail ripped off, another was shreaded. I thought the betta would get along with them? Is it just his personality? i already had to get rid of the one with no tail. What should i do?