Ugh I know right? I had to order in a whole bunch of stuff, I now have two kinds - no three, including Maracyn 2, for internal and external problems, then I have ich meds, then then then x.x all ordered in. But they never seem to come in when I need it the most... lol.
one of my molly babies got mouth fungus. I dunno what it's even from.... other than balloon mollies are susceptible. But anyways, I pulled him out and I did end up euthanising him since I had no meds at the time. All I did was a 50% water change, and since then everyone is okay :) That's all I'd recommend lol.
Same with if one betta girl passes away.. do a water change. that also helps with reintroducing new ones, or getting them to establish dominance.