You can also buy a product made by Wardley
"wardley essentials SMALL FRY"
It works really good even for new born betta's
I don't use any live foods, Just the infushia created by older more established Floating Water sprite.
and "wardley essentials SMALL FRY"
At approx 2 weeks they can start eating very finely crushed fish flakes.
I have had batches that I wasn't aware of survive two weeks on infusia from my watersprite alone,
I do however keep my spawning tanks covered in mature watersprite, More plants mean more infushia,
I also try to get the watersprite to get a greenish algae all over it's top if possible.