Update:
Day 16: My GATF still NOT accept food stick and killed another barb (barbs are 3 inches)
What's other fish can be a teacher fish with less being kill by my GATF? he's already killed 2 barbs so he will kill them again and again.
How big are the barbs compared to the gatf? I got barbs that are 2" compared to my 5" gatf. I recently got 1" barbs and removed the 2" cause they were eating the food and the next day one of the barbs had a giant gash in his body. Do you turn the light off at night?
Do you have any current in your tank? Temperature should be at 85F