are they feeder guppies? i did not realize they were in the tank, not that it matters. . . i'd probably keep them in there. one day, you will awaken and they will be gone. the knife or the pacus will make a snack of them.
Guppies are all around bad for your fish, not alot of nutrition, possible diseases and parasites, and they are messy. I would recommend either getting rid of them or hoping the best. I started the hobby not to long ago and I have learned so much from MFK and from personal research so I can assure you will get the hang of it in no time and have fun at the same time.
Welcome to MFK asap you would want to get them off of feeders.. just simply because feeders offer little nutritional value but mostly because they introduce disease.. but i think the most important thing right now is that tiny little knife eats something.. so tiny little guppies are a must... and also keep trying the blood worms.. maybe use an eye dropper and point it right at his face.. then later once he is bigger and stronger you can wean him off live and get him on a good healthy diet.... CK's are from the wild so he is jus use to eating live..they are not bred in captivity so they take time to wean over....but this guy is too little and fragile right now..good luck..