Had a marine betta in my first two tanks, a 75g upgraded to a 180g, back in the late 90's. Loved that fish! Was recently researching if it would be a good addition to my current 120g, and found out that the fish currently in that tank (a latticed butterfly, rusty dwarf angel and solarensis fairy wrasse) are much too aggressive feeders to allow the betta to get a good meal. Our current fish also utilize all the caves, and I believe they would seriously stress a betta with their territorial behaviour. As a result, we passed on getting another one
For the most part, marine bettas are solitary fish that spend their time in a cave of their choosing. They are diurnal, and feed best at dusk and dawn when they are naturally active.