I had a male and a female in my 75, for a bit. I had a lot of hiding places for them. When they did confront each other it was brief and just a little flaring and they separated. I took the male out when I added more females. The reason for this was I put a male in a twenty gallon with two females, just for a few hours while I worked on their tanks and the beat him up bad enough he died a day later. The moral of the story, bettas are unpredictable sometimes it could work, other times no. I wouldn't try two males in a small tank, though. My 75 is way more heavily planted and decorated now and I still wouldn't try it. I could see it working in a six foot or eight foot tank that was very heavily planted and decorated but the last time I posted that question, the general negative consensus was one tank, one male, no matter how big.