Here's a guide (from my experience). Please pardon any spelling mistakes.

Breeding Betta










Separating Sexes.
Around two to four months, males start developing brighter colors and slightly longer fin extensions.  If you keep lots of them together, they fight a little bit, but not much.  Once you separate your males into individual containers, they start wanting to fight.  Many females also get very aggressive when you separate them.  And some females fight when kept with other females.  These are guidelines, not rules.

Change Your Water. 
Weekly water changes will make your bettas grow faster.  So will larger containers.  So will frequent SMALL feedings. 



Feeding guide:
Option # 1.  Feed them Infusoria.
Breeders who start their baby bettas on infusoria usually rear 90% of their spawns -- some 400 to 600 babies.  Get your cultures started at least two weeks before you set up your breeders.  Raise it in non-aerated quart jars filled with aged water. 

Option # 2.  Feed Newly Hatched Shrimp. 
Breeders who start their betta fry on newly hatched brine shrimp will rear spawns about half the size of those who start theirs on infusoria.  Try your hatching methods early so you know they work, and you know your “eggs” (really cysts) will hatch for you. For best results, feed infusoria their first two weeks and start adding brine shrimp their second week.

Option # 2.5.  Feed Microworms. 
Possibly better than Option # 2.  Use same as brine shrimp.  Better, use Option # 2 and # 2.5.  Best, go with Option # 1, then add #2 and # 2.5 two weeks later.

Option # 3. Powdered or Liquid Fry Food. 
You will successfully rear about 5% to 10% of your spawn if you start them on powdered or liquid fry food -- about 50 bettas.  Your betta fry don’t eat those foods.  Actually, the infusoria naturally occurring in your water eat the bacteria that eat the liquid food, and the baby bettas eat the infusoria.  There are just not enough of the infusoria surviving this way to feed many baby bettas.  Only the strongest survive.

GOOD LUCK BREEDING!