Cory with missing tail?

[defyentropy]

Hi all. I bought three cories a few days ago, and they've all been getting along just fine. 1 green, 1 peppered, and 1 albino.
However, I just got home from work to find the green cory missing his tail fin. It looks like it was just kind of chopped off at the base of his tail, just a stub. Doesn't look particularly shredded. He's skittering around a bit, but hiding as much as he can. My albino is also staying very still and the peppered is staying in a cave, while all three had been very active up until today.
10 gallon, also in the tank: 1 male guppy, 1 female guppy, 1 female molly, and a breeder net with some guppy fry. I also lost a male guppy a week or two ago to fin rot after someone nipped up his tail.
Is this a case of a bully in my tank? The molly is the biggest by far, but I've never really seen her go after anyone or nip at anyone. I don't have a second hospital tank to put anyone in. Any suggestions? Is there anything else this could be?
Also, as for the cory, I've taken out the carbon filter and dosed with melafix. Is there anything else I can/should do?

[Cory]

I am curious. Do you have new updates ?