He's gorgeous! Male and female bettas should never be housed together even if it's a big tank. They are extremely territorial fish. Phoxly just meant you could've had an all female sorority of 20. You can have females together, it just has to be a group of them to level out the aggression. He's going to be a VERY happy betta!
55 GALLON! Dang! That is one lucky Betta! Good idea with the rock formation,
just make sure its safe and he couldent get hurt in, out, or around it. Oh and I agree, NEVER house male and females together!
How do you think they got they nick name as siamies fighting fish?