Hi, just coming into this late. Lots of talk about carbon, but remember that carbon doesn't remove all chemical toxins. water changes do. When I have a case of acute poisonings, where fish are dying, I perform a series of water changes that get me to a total of 100% Then using carbon to take care of anything left (three 33% water changes don't give you an effective 100%, because the second and third changes are also changing some of the water you had already changed). Do I understand though, that you aren't the primary keeper of this tank? Doing big water changes can be tricky if you don't know how.
Circling back to the animals: all the fish died? How many invertebrates died? What is left alive? Is more than one coral looking bad?
Jay