May I recommend a salt bath for 30 minutes or more rather than actually dosing the hospital tank with salt. Most likely more healthy and comfortable for your little guy. Also, there may be a bacterial infection secondary to a fungal infection. I've heard of a case such as this where a fungal infection could not be treated successfully with Maroxy due to an additional bacterial infection. Maracyn 1 was used to treat the particular infection I am speaking of successfully- although some infections may require Maracyn 2. (each targets a different type of bacteria) Be careful when using either type of Maracyn, as they are known to have a negative effect on the beneficial bacteria of your tank in addition to bad bacteria.
Is your little guy still eating at all? May I also recommend moving him somewhere warm if you are unable to heat the hospital tank, as these little guys do not do well with temperature change/shock.
Are your water levels normal??
hope this helps, and good luck to you.