Our Gray Tree Frog seems to be showing signs of advanced MBD. Can we reverse it?! Help!

He is sitting on the bottom of the tank, unable to move his back legs. They lay limp. It still appears that he can still move and kind of get his bearing with his torso/head. This advanced stage happened very quickly. One day he was up on the side of that tank like he usually is, the next day he was sitting on the bottom, not moving. It has been three days, he is moving less and less. The back of his body is starting to look bloated. I want to save him and have him back to normal.

Is it too late? Can we reverse it?!