Your ammonia levels need to be reduced. start by doing a waterchange and see if the RTC responds to that. the skin problem could be caused by a number of things, my best guess(which isnt a good guess) is flukes or lice. I can see in the first pic that its bottom barbels are rotting.
You should do a wc in the time being, then re test all the parameters of the water and let us know whats what.
Also, would like to know tank size, fish size, is the fish still eating?
If your fish is still eating, there is hope for it.