I'm sorry no one came to the rescue but I'm sure a lot of people saw your thread but honestly did not what to do. Just now looking over the thread, you seem to be doing everything right so I have no idea what could have happened. But it could have benn a terrible infection that couldn't be stopped. I'm sorry for your loss but at least you know that you gave it your all for him. I was crushed by my first betta dying and I too did everything I could but the terrible infection finally took him. I was really really sad but my parents said "You did everything you could have done but sometimes life passes. That's just the way it is."
~Budgies and Bettas~