I just want to clarify this for future people reading it, or if youre still thinking about it.Half liter for each betta at 3 months of age is enough... do you think 3months old betta would be as large as matured one? Because I don't think so, if you have ever bred Bettas and you isolated female using jar or bottle that only proves that you are wrong as the jar does take up to 1 liter.
I just want to clarify this for future people reading it, or if youre still thinking about it.
Having bred bettas 1/2 liters are too small, and bettas are full grown or nearly full grown at 3-3 1/2 months of age. If you would look on aquabid you will find people all sell theirs at 3 months full grown. Please rethink breeding them