Elephant Nose Fish Battering Neons - Reason For Deaths?

[TRAGICTRAMP]

I was just watching my fathers tank which until before the weekend was having daily deaths mainly his neon tetra's, and within 20 seconds of the light being switched off, i noticed 1 of the neons started spiralling out of control and into the flow of an airstone, on switching the lights back on we noticed his elephant nose fish going beserk and smashing the neon about the place like a dolphin would and almost throwing it out of the water. I also have an elephant nose in my tank, but mine will push other fish out of the way including my climbing gourami, and usually only if they are in his space or its bloodworm time.
 
Is this quite common? the link below shows the deaths which have ocurred, all when the lights are off.
 
http/www.fishforums.net/index.php?/topic/415219-fish-dying-daily-water-tests-perfect/
 
cheers