You cannot use Melafix, Pimafix, or Bettafix on any betta, gourami or any other labyrinth organ fish for any purpose anyway. It damages their labyrinth organ and will eventually kill them.

I guess all you can do then is to try to wait it out and see by putting one piece of food in the area where you have him to see if he will eat it for you but you will have to remove it if he does not and if he is still in that bag he will have to have water changes as it is unfiltered and his ammonia levels will be growing.

While I do not like the idea and it is a hard thing to do, if he does not improve in a couple of days, I am thinking that you need to think of the possibility of euthanasia for him. He is not going to be able to continue this way for a long time and he can be painlessly put to sleep if he does not improve. But he can have some more time to see if he will improve if you would like. I have some methods that would be painless to put him to sleep if this is what you decide to do though.

Rose