And so it goes with attempts at medicating fish. Without proper identification of what specific pathogen ,bacteria,or fungal infection is present most hobbyists can only make their best educated guess given the symptoms that are observed. Proper identification would involve microscope to observe samples of feces or scrapings done to determine exactly what the offending organisim or pathogen is and most hobbyists don't have the means to do so. It also requires the ability to identify different parasites from one another when looking at them.As hobbyists we are lucky in some respects that medications offered have wide ranging capabilities when addressing some parasites but other medications, are for specific applications and affect different fish in different ,sometimes,harmful ways. As I have said many times, It is ALWAYS easier to maintain the water quality than it is to treat sick fish. Proper feeding, water changes done regularly,properly stocked tanks, and the ability to identify possible sick fish when purchasing them = fewer sick fish. When fish are stressed for any reason. their health will suffer as their immune system is weakened due to the stress and thus disease and Illness are more prone to present themselves.
And sometimes despite our best efforts fish die.