I know they are nocturnal and have moon lights for this. these fish rarely grow over 15 inches in captivity and upgrading the tank is not a problem, Should this be an issue! I was not asking whether i should get a ghost knife fish, as i have kept one b4, i was just asking for an idea of what people recommend to keep with them. I can`t believe how quick you are to judge and dismiss me, with out asking if i was prepared to do what ever it takes to care for a bgk! If you had some constructive advice i would like to hear it. If all you are going t do is tell people "don`t even bother rather than to look after this fish are you prepared to do this........... think b4 you buy, If you can do this then fine you are a good fish keeper!" Then just don`t bother. Thankyou to everyone that has given good advice, I feel you can always learn from other fish keepers!