Do you have a bucket you can put him in? Make sure it has never had soap in it before. If you do, fill 'er up with water and try to add an airstone, and quarantine your danio in that. It's best to treat fish in a quarantine tank unless many ifsh are showing symptoms.
If you don't have a bucket, is there any way you could buy a small tank? A bare 10g tank (no hood, etc) goes from around $10 around here. Again, just add an airstone (although a small filter would be better) and you're set.
To treat fungus, you can use any of the following:
Depending on how much your fish are affected and if you have any other fish that you dont want to get affected, you can hopefully have them settled in once you have made sure that it is decloranated(?) and that the temp. is ok.
If its just one little danio you don't really need to wait very long. As long as temp is stable put him in and treat with either the medication listed above, or you can try and use some jungle fungus fizz tabs.....they work amazingly fast for mouth rot.
