oh **** your right..... lol forgot about the nocturnal part... Hmmmm What do you suggest..? Just not keep the knives with the africans? Take the knives back? Damn I really like the look of them lol...
Well, you have two options, keep them with tankmates too big to eat (3"+ to be on the safe side) / keep the knife fish by themselves or get rid of them unless you want to risk feeding them expensive feeders lol