At this point, I am not thinking myco. It could be another bacterial - or parasitical infection.
I'd go the Kanaplex route first (bacterial). Then try something like API General Cure (parasitical). Actually, I wonder if you can use them simultaneously. (I'll look into this.) If those don't work, I'd look for oxytetracycline and/or Romet.
Edited to add: Yes, it looks like you can use Kanaplex and General Cure simultaneously. I would go ahead and do that. This will give you a good antibacterial and antiparasitical combination. I found multiple websites saying that it was OK to combine the two meds.
(This web site
said you can even combine Kanaplex, General Cure and Furan 2. They said the combination of all three was previously available in a single product, but that company went out of business.)