When medicating tropical fish, there are really only two things that a hobbyist can diagnose and successfully treat – ich and fungus.
Trying to “cure” other supposed diseases by using antibiotics is really foolish, because a) unless you have a microscope and know how to use it you won’t know what the pathogen is, and b) in knocking out the bad bacteria you also knock out the good bacteria of the nitrogen cycle and then pretty much have to start from scratch.
Most problems with tropical fish have to do with water quality, and a couple of partial water changes will usually do the trick.
That said, there is one other thing having to do with medicating fish that really bothers me. Some hobbyists have picked up the idea that on “sensitive” tropical fish they are better off doing half doses of medications. While I know that QuickCure (formalin and malachite green), which is the most widely used cure for ich, cautions to use half doses for scaleless fish like loaches, I have never found this to be necessary. I use QuickCure at full strength whenever I receive shipments of tropical fish, do a water change, or move fish from one aquarium to another. I always use a full strength dosage. Same is true with antibiotics. Using antibiotics (which I do not think is really needed for hobbyists) at half strength also makes no sense to me. It will not achieve the cure that you want, assuming you have stumbled on the right antibiotic. All it will do is to create stronger strains of the bacteria – strains that will become resistant to the antibiotic.
In the commercial ornamental fish industry this is happening at an alarming rate. The ich protozoa has evolved into a new strain of “Super-Ich” that does not respond to QuickCure or copper, the two most commonly used cures. Quinine is the only remedy for the Super-Ich. Treatment of commercially raised tropical fish with the most common antibiotics (tetracycline and triple sulfa) is in certain cases not as effective as it has been, as the bacteria have evolved resistance to the drugs.
In summary, I really do not think that medications, when they need to be used, should be used in anything other than the recommended dosage. The dosage must also be carried out for the specified number of days, even if the tropical fish apparently have overcome the malady. And also, I am really against treating sick fish by raising the temperature and using salt, as it just doesn’t make sense to me to stress fish that are already stressed by disease with other stressors such as high temps and salt. This is especially true when we have medications that work well, and do not stress the tropical fish as much.