Hi,
You list ammonia and nitrite but not nitrate. Have you checked for nitrates? What is the temp?
Whenever mine get skittish the first thing I do is to raise the temp to around 88 and add 1 TBS salt per 10 gallons. This helps most of the time.
Is there anything creating a vibration near the tank? Slight sounds to us can be deafening to fish.
Stray electrical current in the water?