Man I don't know.
Just going to toss some more ideas out.
If you have hydrocarbons/poison from a bug bomb, although unlikely, I would do as suggested with many routine water changes, run activated carbon, changing it daily, and a polyfilter.
If your pH is good - then that would rule out a faulty CO2 component on your calcium reactor.
Ammonia nitrite levels zero would make me think your biofiltration is in order.
Nitrates a little high, but not toxic to fish.
Several fish and corals all dying around the same time makes me think that something toxic has entered the tank. Something we don't normally test for.
Can you think of anything that is different now, that has changed prior to you having these troubles ?
Additives, circulation, having strangers in the house. Did you leave a dirty powerhead out for awhile then add it back to your tank.
I dunno - now I'm grasping for straws.
