From my experience in breeding betta fish, I would like to say that Moina (water flea) is the best for raising babies betta fish. If you can't find it , you can't success in breeding the betta!
I used to try other food also, but all others failed...I can't get a lot of babies bettas alive as much as using the Moina. The babies grow very fast if I give them Moina.
Even if hatching artemia's eggs then give the babies is also good but it can't use more than 2 weeks because once the babies growing - they will show strange swimming manner due to the result of salt.
So in summerize, no water flea - also no my bettas ^____^