I've had a male Betta Fish in a 20 gallon fish tank for about ... 1.5 months. I was loosely monitoring his behavior and condition, as I had just gotten him, and noticed that he remained frantic in his patrolling, although his health was improving. I thought it would ease over time, as the tank had hiding spaces and tannins, but no go. I then moved the sponge filter and plants into a 2.5 gallon I'd had as a quarantine tank to see if it was a tank size problem. He was slightly less frantic. Last week I moved him into a 5 gallon tank, with same sponge filter, plants, terra cotta disk ... and he is calm and exploratory. Apparently the little dude just needed exactly 5.5 gallons of water.... Someone on here posted a while back that one of their betta seemed unhappy in large spaces. I'd never experienced that until little dude. I now wholeheartedly believe you, fellow fishlore-ee!