Nipping Or Fungus

In my 5 gallon tank I have two Black Skirt Tetras and a Serpae Tetra. My two Black Skirt tetras have fins that are splitting and, well I don't know; their fins look terrible. I've tried medicine for fin fungus and something else for bacteria months ago with no improvement so gave up. I've also seen them nipping at each other. I'm looking to add another fish to my tank. Is it safe to add more fish to my tank? Here are some pictures. Is it nipping or fungus? How should I treat it?

 

5 gallons is not big enough for these fish. Additionally these are schooling fish that need more of their own kind. Skirt tetras are notorious fin nippers, so they are probably acting out due to their conditions. Moving them to a larger tank and upping the numbers of each to at least 6 should help. A 20-29 gallon tank should work I believe. But additional research may be need to verify that

 

Its from nipping. You need to get them into a larger tank ASAP and up the schooling numbers. Or rehome them.

 

These kinds of fish are known to be nippers. I haven't really experienced any nipping yet anyways.

You shouldn't be worried about fungus unless there is signs of it or you didnt fi your cycle

 

Thank you everyone! They are in a larger tank now and will be joined soon by some more!