shrimplets growing slowly...

Hi there, i have a couple of batches of shrimplets and i observe them daily, think is, they don't seem to be growing a lot.

they're feeding well,(the larger ones are able to join the adults during feeding).. the small ones just pick off algae n such from the glass or mosses.

am only dosing minute amounts of mosura mineral plus... should i buy mosura exel? How do i ensure that the shrimplets are getting the nutrients they need?

thanks!