The fish is now on its back but yet still alive.
May be to late, sorry to say. I would like to see you move him to
qt, but it would do more harm at this point.
Is there anything I can do to help?
Do a good size water change with some well aged and airated mix, keep water quality high.
Is usually a physical injury.
Depends on where they get their stock from. Many times these fish are cyanide caught and are doomed from the get go. I would definitely try another store. See if they will allow you to leave a deposit so you can observe the fish for a week or so. At the very least make sure you SEE the fish eat before bringing it home. Also a
qt tank is ideal for new fish. In a
qt setting, you may have been able to treat the fish more effectively and also keep any ailments out of your display tank.
Good luck, I hope he pulls through.