Clown trigger dead

I'd say you had a sudden parameter swing that messed up your fish. They shouldn't have a problem handling slowly increasing nitrates, or slow changes of almost anything. Its the sudden swings that can cause havoc to a tank. Have you been moving anything around lately? Adding anything to the tank?
What I might suggest is just stopping everything but routine water changes. No additions, no moving stuff around. Nothing but leaving the tank alone and changing the water as needed. Let the system stabilize and mature for a little bit, then slowly start make changes down the road awhile.
Nothing good happens fast in the world of reef keeping.