Cannot be an ammonia precursor problem, ruled out for sure.
Nh3 are by rule tank wide events. Inability to molt is more likely/ alt causes. It takes massive insult to get nh3 cycling, and outcomes do not require any test kit to spot. Post pic of your tank we love ammonia tracing work!
Here's a legit tank wipe by nh3:
Recently had a huge leak in our 90 gal reef which forced us to upgrade sooner than expected . The upgrade being a 230 gal with a 48 gal sump . Mistake #1 I added some of the old sand assuming it would be beneficial to have a little bacteria .. I was wrong . Nuked the whole tank killing all fish...
www.reef2reef.com
Cause: added unrinsed old tank sand. And it would take a lot of it, clouded with gunk, to over come natural nh3 controls its the #1 parameter every reef post cycle never fails to control.
Working seneye machines have tracked out dead tangs left to rot, thousandths ppm never veered. It takes massive insult to kill something with free ammonia