okay i have currently a 75 gallon tank with 1 silver tip shark, 1 bala shark, and 1 Senegal (dinosaur) bichir. I use to have a black ghost knife but the bichir killed it..... The bichir was like 4 inches. the black ghost was 2 inches. Why did the bichir killed it??? Also i might get a tiger Oscar. a baby one.