I will throw a couple thoughts out. Considering a lot of your CC died, I would be wondering why. I would test the water to see if anything really jumps out as potentially bad. Were the CC 16" when added? The bigger the fish, the harder to transfer successfully. Did the CC have anything to eat once in there? If not, self explanatory.

If it were me, I'd buy some FHM and throw in there to see if they live and multiply. Just make sure that each and every one you add is truely a FHM!!!!! That means hand sorting every one.