I have 2 black ghost knives in my tank, and am wondering what I can feed them, and also, will they fight with each other..?? They were in the same tank in the pet shop, and seem happy in the tank together.. They are in there with my female guppy, but she just hides at the top corner of my tank next to the heater.. She was there first so will they try and fight her for the territory, or will they just leave her alone..?? They dont seem bothered by her at the moment.. They came home yesterday..