How do you prevent your fish from nipping at each other and treat the injury?

I have had 2 fancy male guppies since Easter and now out of nowhere they are starting to nip at each others tails. (And damage to one looks pretty bad!) I am not sure if this some type of aggressive behavior or a sign they need new "friends". Theyre also probably about ready to breed but I am not going to add any females, so will this behavior continue? Is there any way to prevent the nipping? And how do I treat the torn tails or fins? Is there an ointment or drop that goes in the water? I added 2 new fish - blue lyrletail delta male guppies and the problem is now WORSE! I think they even killed my bumblebee catfish! I dont have another aquarium so I cant seperate them. I could go buy one but someone may not make it overnight in time.

seperate them into two different tanks

it could be agression, but i would try to change the tank around, so they can establish new territory. if it is aggression, then they need to be seperated. as far as helping them heal, i would get some salt from the pet store for your tank, and also melafix. just follow the directions on both of the boxes, and if you can...put the hurt one in a different tank

well you need to separate them maybe its their time to breed so they are getting agressive but separate the tank into 2 and that should solve the problem. and for the medicine, i think the tails grow back by them selves

It most likely will as long it is just two males in the tank. If you have two males you should get more fish to even out there aggression. I had 2 black skirt tetras in my community tank and one was being pick on so much he almost died, so I add 3 more. They are all happy and most of all the other fish is healthy again.