Get a small pestle & mortar & crush up flakes or pellets for them.
Imo bought fry food is ok for the first few days, but after then they need more than that
I feed liquid fry food for 2 days and then crushed flake, i feed mine 3 times a day, the ones in my small fry tank are growing slowlly, the 2 that i couldn't catch that are still in my big tank are 3 times bigger (and only fed once a day).