Buy terra cotta pots and clean them with hot water and let them soak overnight. Fish like to hide in them. There like caves. Fish also nip at each others fins. It happens as a result of a space issue most of the time. Just get some if the pots and lay them in their sides like caves. I was suggesting something small when it comes to separating the platy, such as a breeder net or a tank divider. Not something that would stress him out too much.