'Nightcrawlers' are our lobworms .... you've already got what you need. As for the slow starters this may just be par for the course. You do get some that never catch on. Tetrataenia can be very tricky due to the amount of inbreeding in the available bloodlines which has resulted in smaller offspring/litter sizes and failure to thrive. If you're breeders are brother and sister then I would sell all the offspring singly to make others source distant relatives from another bloodline .... I would also look at replacing one of the breeders with fresh blood.