Daily water changes will speed up growth.
Also, 40 fry is a lot. What size tank do you have them in.. A bigger tank will speed up growth once the fry get to a certain size.. If they are in an undersized tank, water change as much as possible, maybe even more than once a day.
Also, see if the fry will eat something larger than baby brine shrimp.
See if their bellies are stuffed after feeding.
