Dead Bursa Trigger

[Johnny Reefer]

Woke up this morning to this:


Not a spec of physical damage or disease anywhere:




I'm at a loss as to the cause. Parameters were tested a few days ago.
pH 8.4
NO3 35mg. (High, yes, but a predominately FOWLR tank should handle it).
PO4 0.25. (High again, but tolerable, no?).
Alk 12.7dKH. (At the high end of the scale, but not extreme).
SG 1.022
Temp this AM was 79.5F

I have no clue what could have caused this. This fish was eating with gusto just 12 hours ago. Now dead. All other Triggers are fine and acting normally (Clown; Pinktail; Humuhumu; Blue Chin).

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