Ouch man.
I feel for you. I hate these events .. the worst is when you don't even know why so you can't even think of something to do differently in the future to avoid it happening again. I had an event like that in September. Never did know why. Thought it could have been a clam or anemone spawn but have had both spawn before and never was fatal, and besides none of them had that "spent" look so I never could be sure that's what it was. But I lost 4 fish that day.
Sucks.
Anyhow point being, I feel your pain.
Good luck!!!