When I had my 20 gal, I put my wife's betta in it with my Bolivian ram with various tetra and they coexisted without any issue. At least that was the case when I was around. The betta wasn't they long. Just long enough to cycle the gal tank at my wife's classroom. Every betta my family had never had issues with being in a community. But perhaps the betta and the Bolivian were fine because the betta pretty much stayed near the surface and the the ram stayed at the bottom. In my 55 gal tank, my German ram goes all over the place.