My tetra's fins are missing!!!!!!!!!!!!!!?

i have a 55 gallon tank with 7 guppies, 14 orted tetra, and 2 ram cichlids. i woke up this morning and inspected my tetra and my glolight and neon tetra have pieces of their tail fin missing. What could this be i have never had a problem with this before could it have been my rams. I have never actually seen my rams show aggression towards an of my other fish. I added melafix to the tank a few days ago but that was due to one of my rams suffering from fin rot. Could the melafix have had a reverse reaction. My guppies and other tetra are fine but only the neons and glolights are hurt. I also have black neons and serpae tetra. What is it?