How do you dose Wunder Tonic topically (directly to the fish)?

[Plecosaurus]

I've just come back from a thread from like 2008 saying that Wunder Tonic can treat columnaris, as well as Furan-2. I already have Wunder Tonic and already used it and it didn't help my fish, but I am pretty sure they have columnaris so I assume applying the tonic topically like mentioned would help better since it's direct? If so, do you just put one drop on each side affected on the fish? I have neon tetras if that's any help. So I don't think I can use salt for them? I didn't want to risk it since I am unsure.

I can get the Furan-2 if that's going to be better, but unfortunately I don't have a lot of money right now so it'd have to wait about 2 weeks which isn't ideal since I have already had fish die (I have been on a wild goose chase and fish stores have wrongly diagnosed and prescribed medications that haven't worked, I have tried 5 different ones so far!!) so if I can avoid spending anymore money then I'd like to :(

Thank you :)

[alanmin4304]

What are the signs of columnaris on the fish? Are you sure that is what the fish have? Dosing directly onto the fish is not likely to be effective as the infection will be in the water.