There are also medicated foods since the fish is eating. I've gotten them from angelsplus. But you do need an idea or good guess of what might be the problem to know which to choose. I'd think if 1 fish has whatever, all the same species bought at the same time would have some level of the same thing. & so might any other fish in the tank by now.
Fenbendazole needs to be fed to work, but it's similar to flubendazole. I don't recall the brand but there's prazi/metro combo med, I haven't used it. Levamisole I have used but it doesn't kill the eggs so needs to be redosed in ~2 weeks. It's fairly mild compared to some meds IME, but some fish may be sensitive. I often treat wild caught loaches in quarantine "just in case", but add half a dose in the am & half in the pm just to be extra safe. I "think" it's capillaria it treats.
It helps a lot that you can look under a microscope, but in a decorated tank it'll be hard to get a sample, lol. Yes, a bare hospital tank would help.
I'm still hoping it's the blood worms... & whew, it's not camallanus, those are thin red worms & more difficult to treat IME.