Hi,
I am not sure how good/bad the treatment you are using will do as by the sounds of it its for fins so you may find its not doing very much for this fish apart from relieving you of a few ££
Personally i think you will need to have the fish out and give it a good clean up and treat it topically to give it a good chance of getting on top of this. Time may be against you depending on if you are heated or can get the fish into a hospital tank of some kind as we will be coming into winter very soon and these things are best done in warmer temperatures.
First off you will need to sedate the fish and work on it so a nice clean area with a baby changing mate or some wet towels all ready to go and a bowl to sedate the fish in. Make sure you have everything to hand ready before you start then you will not panic. Sedate the fish and place a wet towel over the eyes and tail which I find helps keep them calm.DON'T PANIC!!!!!!!!!!!!
You will need something to clean the wound like Rocal or HP (Hydrogen peroxide) if using HP make sure you do it with a cotton bud and only get it on the wound as it will damage other skin and position the fish in such a way you cant slip or drip into the eye. Just add some HP on a cotton bud and be very careful not to get it onto any good skin or the eye when on the wound you will see the HP fizz and once done dry off completely. You will need to remove any dead and decaying skin or damage making sure all that is left is clean wound and tidy and dry.
Once this has all been done too will need to no use a topical treatment which you will need to get from a dealer or on line dry good seller. There are many out there and I like to use Mecurochrome 2% and all you do is apply over the wound and then let it dry and if you can I like to do this a few times.Again try to position the fish so you don't get it in the eye.
I would also seal this off so I would then one the topical is dry add a sealer like lock and seal and also sprinkle Oraheasive powder on top of the seal while it is wet then blow off the residue powder and put another layer of lock and seal or a sealer over the top of the powder.Again keeping any treatments away from the eye.
The next thing for this to help heal is your water needs to be spot on and clean so making sure you clean the filters when required and carry out water changes is a must as the cleaner the water the more chance on the fish healing easier.
Heat is also a great help with these things so if you QT is nice and mature and you can heat it up this will also help and you could also if needed treat the QT with some CT (Chloramine T) which is a great tool at knocking back these types of bacteria in these situations.
Hope this helps and good luck and please keep us in the loop on how things go.