A: Aoutch. Does not sound too good for Mr. Betta. If you are sure your water is not in question, then one of two things could be at play. Either parasites or bacterial infection. If you shine a flashlight on him do you see either white spots (ich) or a gold like all over very very fine powder (velvet)? if so, treat with maracide or any other velvet medication. A water change and sanitization of his home first is a must. In my opinion you will not see either because I think you are dealing with a bacterial infection. You mentioned antibiotics but did not mention which. I would go with Spectrogram or Kanacyn, double dose. Have you fed live foods? If so, your supply may have been infected. I think your betta only has a 20% chance of recovery, but don't give up! Do double check your water, make a full water change (very gently) and also make sure there isn't anything in the tank that could have contaminated the water (any metallic object, sea shells or coral, any harmful household cleaning chemicals, soap etc...). Goodluck with Mr. Sickly Betta.