That would depend on what adult fish you have, the tank size and amount of rock work. Also filter type can play a role as i routinely have fry going over my overflows.
Acei tend to be fairly peaceful so if they are the only adults in the tank and there is plently of hiding spots for the fry they should be alright no matter what the size. i would however expect some loses. But again it is also dependant on the above and probably other factors which i overlooked.
josh