Assuming it's not TB, and that's hard enough to diagnose without the blurry top down picture you have (not a slam, just factual), it looks like open ulcers covered with a bad fungus infection. Is he hovering at the surface swimming in circles? Not gulping air, just swimming under the surface all the time. Is he eating?
You have to remember that scaleless fishes suffer the most with bad water parameters and even after that has been corrected, it may have already compromised their immune system so that they pick up any bacteria floating in the tank.
He looks pretty bad. Isolate that guy asap and start a regime of anitbiotics - tetracycline, erythamycine. If you salt, do so lightly and warm the water up -- not too much, don't stress him. Change the water often and redose to keep the levels of antibiotics up.
Give it your best shot.
Roan