Well by now it certainly seems that the traditional treatments/medications are not having any effect. If the hole is bigger, and deeper, as you stated, then that means more tissue is likely dying. I suspect that if you placed a swab of that tissue under a microscope you would find bacteria at work. What Diesel recommended could very well stop that necrosis in it's tracks, allowing new tissue to grow back. Or, you could keep trying the more traditional treatments.
Your fish, your call. Good luck.