So I've had my male betta fish,Jack, in a ten gallon tank with 5 neon tetras. (I had six but one died a week or so ago) There has never been ANY problems at all with them. There was no chasing or any fin biting that I could see. Last night I saw jack chase a neon around the tank....I thought that was really strange but didn't think much of it. Later, I saw jack chase one of them and neon practically jumped out. I was starting to get worried so I sat down by the tank and watched them for awhile. Then to my horror, I saw jack jump at one of the neons and bite him. More like rip a piece of his back fin off. I was in shock Jack has NEVER done anything like this before. The neon is fine...swimming around pretty normally, so anyway I asked my sister to keep an eye on the tank while I went downstairs and got one of my extra bowls ready for jack to stay in over night....as I was cleaning the tank my sister started yelling that Jack just tried to "eat" one of my neons. I ran back up and sure enough jack just again attacked one of them. So I quickly got jack out of the tank and put him in my spare bowl over night. Today all the neons are fine and so is jack but I am VERY confused why Jack all of a sudden has a problem with the neons they have all been in the ten gal together for a few weeks. Any ideas on what happened? Should I try to put Jack back in or get him a new home?........HELP!