My fiance has a 10 gal . In it were 4 guppies, and 1 bronze cory, and 1 albino cory. Tuesday I bought him 2 female guppies, and he bought a female guppy. He took them and the albino and bronze cories from my tank that had 3 fancy guppies, 3 common guppies, 2 female bettas, and 3 spotted cories. He texted me about 3-4 am this morning that one of his cories was attacking one of the female guppies! the cories had eaten the fins completely off of one female and were chewing on the other. He's been feeding mostly betta food (he has a solitary female betta and his dad gave him the leftover food when his mom's betta died) flakes, pellets, and f-d bloodworms. Any ideas what would cause the attacks?