How to properly pick mdedecine for discus fish:
There are 2 main fish health issues:
Internal parasites:
It could be worms or hexamita. Main medecine to use to treat hexamita is Metronizadole and rise temperture to 92F (and adding more oxygenation like air stone). When your fish is not eating, sometimes you can see hole on the head or around head, white poops - it is time to use Metronizadole. We are adding Metronizadole every 24 hours 1/4 tspn per 20Gal with 25-30% water change before adding medicine.
External bacterial infection
There are a lot of gramm-negative/gramm-positive bacterial infection. So our recommendation is qurantine everything you are adding to the main tank:
Anything you are adding to the tank could bring you a bacterial infection not known to your existing eco-system. What happened next, let's say you got new drift wood or new small tetras, and added it to your tank. It takes 48 to 56 hours for bacteria to grow and start affecting your fish. After few days you already forget what you added few days ago and have no idea why your discus fish started showing symptomps:
For any signs of external bacterial infection you should start treating the entire tank as sooner the better (of course best if you would quarantine fish/plants before adding). We are using nitrofuracin green with proper water change to fix external bacterial infections issues. To have nitrofuracin green or any antibiotic on hands it is good idea.