Thanks Bill, I haven't shot a concert before and it didn't occur to me that most of the frame is as dark as the film base.
I just tried re-fixing one 6 frame strip for 10 minutes with agitation as Nicolas suggested and it worked! It made the emulsion less opaque.
Follow up question: Do Delta and T-Grain emulsion films have to fix longer than Tri-X?
Thanks again for all the quick responses. It saved my only roll of pictures I shot that night of Shonen Knife.