Well I have a cocktail I use as I think it's very hard to determine what's actually wrong if you aren't a vet or a very experienced fish keeper. So if I have issues I'll hit em with following. Some folks say it's bad to use antibiotics if you don't need them but I'd rather have a live fish than a dead one. Measurements are for a 10 gallon tank:
Nitrofurazone - 1/8 teaspoon every 48 hrs
General Anti-Parasitic, Fungal and Bacterial Treatment/Preventative: Combine with Kanamycin or Metronidazole as these drugs work well together.
Effective against gram-negative and gram-positive bacteria. It is useful against many common fish diseases, especially effective against myxobacterial infections, fin and tail rot, dermal fungus, open sores, and vibrio anguillarum. Effective against Columnaris, Flexibacter, Black Molly Disease (Flavobacterium columnaris), Bacterial Gill Disease, Aeromonas, Excess Body Slime, Cloudy Eye, Streptococcus, Furunculosis, Fin and Tail Rot, Marine external ulcer disease and some protozoan infestations. Useful in treating minor topical skin infections of freshwater and marine species.
Seachem Paraguard - 1 capful daily
(Contains...)
Malachite green
MG is active against the oomycete Saprolegnia, which infects fish eggs in commercial aquaculture, MG has been used to treat Saprolegnia and is used as an antibacterial.[5] It is a very popular treatment against Ichthyophthirius multifiliis in freshwater aquaria. Used to treat Ich,
x-aldahyde
37% formaldehyde solution which is universally recognized as an effective medication for the treatment and control of diseases in saltwater aquarium fishes caused by fungi, protozoa, and certain metazoans. Used to treat ich
Seachem KanaPlex - 2 measures every 48 for a total of 3 applications
(Contains...)
Kanamycin
Used to treat serious bacterial infections in many different parts of the body. Kanamycin belongs to the class of medicines known as aminoglycoside antibiotics. It works by killing bacteria or preventing their growth.
API General Cure - 1 packet every 48 hrs for a total of 2 packets
(Contains...)
Metronidazole
Metronidazole is an antibiotic that is used to treat a wide variety of infections. It works by stopping the growth of certain bacteria and parasites. Metronidazole is an anti-protozoan fish medication used to treat hexamita (hole in the head disease or Malawi bloat), body slime (chilodonella), freshwater ich, epistylis in pond fish.
Praziquantel
Used for the treatments of external and internal parasites, flukes, flatworms, and tapeworms.
Good luck sir!