Hello friends I have a red halfmoon male betta and I kept hima alone in his 5 gallon tank because I heard they were mean. Then I got chewed out at my local community fish store saying that betttas are supposed to be community fish so I put him in my 55 gallon community tank where he killed all of my glofish tetras and small fish. Then I put him in my 55 gallon mini monster tank where he did the same thing. Once while my sister was tank sitting while I was on a buissness trip she somehow "accidentally" put him in my payara nursery where he genocided my juvenile payara(last time she's fish sitting). So at 75 dollars worth of fish that he killed I decided to cut my losses and put him back in his 5 gallon betta tank but I still get grief from the employees every time I go to the community fish store and they say I treat my betta poorly by having him solutary. What should I do?