Summarizing, the medications which can be used for freshwater aquarium fish are:
There is one very important point here. These medications are generally the only disease treatments which are supported by science. There are a few exceptions in that there are a some five alternatives to the formalin/malachite green treatment. But there are not options for the other treatments which are supported by the science.
Now if one wants to spend money, one can purchase and treat fish with any of the hundreds of medications whose use is not supported by science. In most cases all these medications are harmless. Burning money is a prerogative in this world. Have at it!
Note that all these medications save formalin/malachite green are very safe medications ingested by humans to treat human diseases and are approved for use in humans by the FDA. So those who say modern medications will kill the fish are simply return to loincloth folks blowing smoke.
Note that none of these recommended medications (other than the formalin/malachite green) kill more than one type of disease organism. This is quite normal for safe and effective medications. They are safe and effective exactly because they only target one type of organism. In human medicine the only “universal cure” with many uses is aspirin. All the other thousands of human medications have relatively narrow scopes of application. Most fish medications are no different.
Note that the “mode of treatment” is important. Many medication manufacturers have realized they will sell much more product if they tell people to put their medication in the water. They do this even when the medication doesn’t work when it is put in the water.
Note that there are very many disease organisms which can cause a variety of symptoms and death in tropical aquarium fish. Many of these diseases can’t be diagnosed even by a well-equipped lab. Even if a well-equipped lab could find the disease, many of these diseases are incurable. Any experienced aquarium owner will tell you that fish die, frequently! And very rarely you can have a unknown disease kill all the fish in an aquarium room. This is just a fact of life.
Aquarium Science Website
The chapters shown below or on the right side in maroon lead to close to 400 articles on all aspects of keeping a freshwater aquarium. These articles have NO links to profit making sites and are thus unbiased in their recommendations, unlike all the for-profit sites you will find with Google. Bookmark and browse!