I've never had any luck with meds. I thought I may have cured a discus of IP with metronidazole, but the fish never properly ate again and I ended up giving it to someone in the reef club who was aware of its ailments and was excited about having a discus in his 55 gallon planted tank.
And to go along with Delta's point #4, that discus was an 80 dollar fish and meds/garlic/etc. kept it alive (maybe), but certainly didn't pull it all the way through.
Same with ich meds. Didn't do anything for me at all.
Only treatments I use are heat and salt for ich and similars.
Like Big Vine, I had neon tetras pinking out and looking squiggly in the spine and I froze them for the good of the others. A necessary variable in the equation of keeping a stable and healthy tank... (these neons picked NTD months and months after acclimatization and introduction)