The only way to fix it is to ride it out and take your lumps. At this point, I would put some poly pads in just to see what they reveal and eliminate all the other obvious causes. I'm not sure how many colonies you have left, but you could try dipping them which may be more stressful than useful. It doesn't appear to be a water quality issue ( unless the poly pads show something) , so I don't know what a large WC will accomplish other than potential stress. You can also frag still healthy colonies and hope some them survive.
It SUCKS bigtime, but there are no easy fixes here and the more things you change at once the further you get from figuring out what is helping or hurting the situation. I just went through this not too long ago, though not to this degree, so I understand completely. All I can offer is that if you keep things stable, some corals will survive and the situation will turn itself around. Good luck and keep us posted.