It could be the shrimp that made them sick. I used to feed my motoros market shrimp but my big female got sick from it and died, For now just feed worms and if they recover tell him to try and get them on pellets, It will take a while but once you get them on it you wont have to worry about parasites. Ohh and very important that when he does water changes to use a good declorinator because right now as they are sick and sensitive the clorine will do more damage to them than usual.