If a bacterial disease is suspected a culture must be made to confirm the diagnosis.
It is far safer to use a non-antibiotic bactericide and only if this treatment fails then an antibiotic resistance test be administered to the fish to determine the proper antibiotic to use.
The appropriate antibiotic should be administered for the correct duration.
This is obviously beyond the scope of most aquarists and many vets. The problem of indiscriminate antibiotic dosing from non-prescription pet store antibiotics is a serious threat to public health and safety as it contributes to the creation of "super-bugs" - antibiotic resistant bacteria.
This would ordinarily not be a problem except for the one genus of bacteria: Mycobacterium than can infect and even cause the death of humans.
This is an extremely serious problem and if we as aquarists continue to abuse antibiotics and more human life is lost our hobby could face some undesirable regulatory hurdles.
In 1945 antibiotics were considered a wonder drug - a magic bullet against bacterial infection. Then bacterial resistance began to be a problem which gave rise to the "super bugs" such as MRSA (methicillin resistant S. aureus) aka "flesh eating bacteria". There are things other than antibiotics that kill bacteria - bactericides - and these should be a first choice. The use of aquarium antibiotics is actually considered harmful now.
Do not work when put in the water, fish have to eat them or be injected with them.
Have been pulled off the shelf in most countries.
They are far more trouble than they are worth. One bacteria - Mycobacterium marinum found in all fresh and salt water not only causes 'fish tuberculosis' in immunocompromised fish but is zoonotic - it can also cause disease in humans. "swimmers itch" is the colloquial name for the skin granuloma that can be a serious problem. Is Harro Hienomaoums reported, it has already cost the life of one man in Germany.