Just the way you said the tail couldn't be used scared me. Salt will help with the healing process. The salt thing from earlier is that, black spot disease usually happens in tank where salt is added. Has nothing to do with it really and should not make the symptoms any worse.
Do the full dose, sometimes if you don't you actually won't help the situation any better. Don't worry about the others they will be fine. It's a type of ick from what I'm reading and they will also have the parasite but will not show syptoms. This is common with ick. Usually scaleless fish get it first, pictus, id's, etc. If you have no scaleless fish, swords, platties, etc. get it first, in my experiences. Put the other tab in now. Wait till tomorrow afternoon and do it again. Persistance is the only thing you can do. Do the water changes as the directions tell you. Did you get Mardel or Jungle? You may have to treat for 2 weeks maybe 3, but 3 would be a drastic case of it. Good luck!!
Do the full dose, sometimes if you don't you actually won't help the situation any better. Don't worry about the others they will be fine. It's a type of ick from what I'm reading and they will also have the parasite but will not show syptoms. This is common with ick. Usually scaleless fish get it first, pictus, id's, etc. If you have no scaleless fish, swords, platties, etc. get it first, in my experiences. Put the other tab in now. Wait till tomorrow afternoon and do it again. Persistance is the only thing you can do. Do the water changes as the directions tell you. Did you get Mardel or Jungle? You may have to treat for 2 weeks maybe 3, but 3 would be a drastic case of it. Good luck!!