I'm not worried that my betta will kill the neons, neons are much faster swimmers. I just don't want them to nip my betta and bully him. The tank in the video is 5 gallons and I have a 6 gallon. My betta is extremely active- he swims back and forth like he's on crack and he's been in my tank for about a month now. I'm just not sure if he'll think he owns the place since he's in the tank first. I dunno what to do if for some reason it doesn't work out, return them?