Mysterious death of all fish in just a few hours

This is a new tank, but I am a veteran salty. The set up is a 120 with dry reef rock, live reef sand, 2 week old instant ocean at 1.022 fully cycled. ammonia, nitrite and nitrate all undetectable. Skimmer and 8x water flow at 78 deg f. 6 green chromis, 2 fire gobies, and 2 shrimp. All specimens were drip acclimated over a 3 hour period. Half acted strange within minutes, and all were dead within 6 hours. Still no detectable ammonia, nitrite. 15 years and hundreds of fish acclimated and I've never seen anything like this. The fish behavior was excessive gilling with normal swimming in mid-watter. Then one by one they got erect pec fins and died. If anyone has any ideas, I'd love to solve this mystery.