Definitely no girls in with the knife. They're pretty good at what they do despite bad eyesight and girls really don't move that fast[especially not when they're comfortable]. Past that, the knife will need atleast a 100+gal tank when it's full grown.
2 dogs, bearded dragon in 40gB, 4 cats[ugh! xD], 2 turtles[RES/Painted sharing a tank with an oscar & jewel cichlid], 1 temporary 10gal "QT" tank, 55gal planted FW community & 15gal nano-reef ... plus a 20gL planted divided betta tank with 4 bettas that will eventually be rehomed and the tank - decommissioned.