Sorry to hear about your disaster. Something similar happened to my 180g a few years back. Turns out something toxic died that I did not notice. I ran carbon in my filtration system for 24 hours then threw it out. I also did several 25% water changes, which added up to one heck of a lot of water in a 180g
Saved less than half of my fish. Corals were untouched. Fish that were affected by the toxin breathed heavily until dead
