jsoong
Aquarium Advice Addict
I use a salicylate kit, 2 reagents. ...
If you are using the salicylate kit, then you are reading free ammonia in the tap water (pretty unusual). <Is that before you add dechlor?> Just to double check your test, perhaps you can test a sample of distilled water to make sure your kit read zero. Using Prime would be a good idea if you are starting with ammonia ....
Use the biggest tub you have as isolation tank. I use a 30 gal rubbermaid as my QT. Those 25l water aging tubs you have would be better than the tiny 1 gal. 3 single tailed goldfish in a 5 is just too crowded & you get aggression issues, etc.
I don't know why the fantail is nibbling on the wounds, perhaps there are dead tissue that he is trying to eat. I guess the best thing to do is just to watch the behaviour for now.