Sorry for not getting back earlier, I have a hell of a time keeping up with all the posts ive been contributing to lately.
er yeah,furunculosis and vibriosis both cause such lesions, often you can tell by the kind of seeping shallow lesions complete with white bacterial plaques. Fungi tends to be raised and fluffier and viruses such as carp pox dont tend to cause plaques. Furunculosis (aeromonas group vacteria)and vibriosis (vibrio anguillarium and various other strains)can be treated by the same medications. Nitrofurazone available in furan meds would be my personal choice, but its very hard to get here.
Failing that its down to antibiotics like oxytetracyline, and sulfamerazine for around 10 day courses of treatment. Its actually quite easily treated and the fish survival rate is usually good as long as the infection hasnt taken too much energy from the fish, or the osmotic balance can no longer been maintained because the wounds take up so much of the fish's surface. Unfortunately these diseases are only treatable by ssystemic internal meds, topical treatments as you are finding are merely wound attention, and while slowing death, dont actually prevent it, or its spread.
The other major bugger is that every med that can treat a fish for these ailments has to be a proper antibiotic, and also kills nitrosoma bacteria, and that forces ponds into cycles, which is primarily why people who chuck in oxytetracycline just end up with an orange pond and dead fish within two days, the fish of course already weak, rarely survive the massive impact of ammonia from a dying pond, and they asphyxiate. Treat the fish in a sterile aquarium, keep the ammonia off them with ammolock for 10 days and use the antibiotic. Outside of the fish the bacteria are more easily killed and a dose of malachite green at a moderate level usually does the job without completely annihilating the balance of the pond. Hopefully by the time the fish are well and ready to go back out, the pond will be purged of infection.