A 29 gallon is far too small for a mixed gender betta splendens tank. Other than splendens, most betta species can be kept together in as little as 10 gallons. For splendens the real question is when is a tank big enough. In the wild, sooner or later a male and female will find each other, so we need to start comparing our tanks to a wild habitat. In the wild, a pond may be 50 feet across and contain a few B. splendens of both sexes. he males only fight when they encounter each other and one or the other soon limps off in defeat. Likewise a non-receptive female may be subjected to serious aggression and need to escape. What we really do not know is how far a male will chase another male or a female that ventures into his territory. A 29 gallon tank is far too small for it to work, but maybe a 6 to 8 foot long tank might work with very small numbers of males and females who seldom find each other. I cannot say from experience because I simply do not experiment that way with my fish, they are my pets.