Here’s the exact situation, you have no free ammonia we can see by the fish and water clarity. All the stuff added is mildly changed from prior condition plus the moving mud, so corals might be mad agreed but not dying
That much rock, sand, motion and dilution will eat up the sandbed ammonia if any within one hour seneye threads show, when they’re literally adding ammonia to a live reef and watching it go down accurately
add nothing more, test nothing more just the water change, easy fix here. The tank is not crashed and the nh3 is fine now.
the tests you are using have a massive long lag time to report accurately, and now they can’t with prime added. Water change, all is well, alk has no bearing here and the water changes will be ideal. It never did recycle. It mildly upwelled waste, a brief spike like an over feeding event, and you don’t have the right test kits to register the nh3 portion of total ammonia accurately but reefs control nh3 just fine, it’s why your pics are normal and only kits caused the alarm