I can't see anything in the video. Perhaps if you make another video it might show more.
Medications can harm fish, especially if overdosed or you use the wrong medication for the problem. Without knowing what the problem is, I can't recommend anything except salt and water changes, which you have already tried.
Interpet Anti Fungal and Fin Rot medication might work but I have no idea what the ingredients are and the company's website and internet isn't offering any help to that either.
If you think the problem has gotten worse and you have the medication and want to try it, then you can. But I can't see anything so would rather hold off adding things until a more positive identification can be made.
If you do want to try treating the fish, see below for instructions for treating and on working out water volume.
To work out the volume of water in the tank:
measure length x width x height in cm.
divide by 1000.
= volume in litres.
When you measure the height, measure from the top of the substrate to the top of the water level.
If you have big rocks or driftwood in the tank, remove these before measuring the height of the water level so you get a more accurate water volume.
You can use a permanent marker to draw a line on the tank at the water level and put down how many litres are in the tank at that level.
There is a calculator/ converter in the "FishForum.net Calculator" under "Useful Links" at the bottom of this page that will let you convert litres to gallons if you need it.
THINGS TO DO BEFORE TREATING AN AQUARIUM
Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.
Do a 75% water change and gravel clean the substrate. The water change and gravel clean will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.
Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.
Remove carbon from the filter before treating with chemicals or it will adsorb the medication and stop it working. You do not need to remove the carbon if you use salt.
Increase surface turbulence/ aeration when using salt or chemical medications to maximise the dissolved oxygen in the water.