I just was follow your link about fin rot for your new betta and i am completelly agree whith BETTACHKALOVE advice. For the tank size that you have i would not bother to have the filter. Filters absolutely optional for betta. And that filter really strong and pushing him around that makes him stressed. I would take the filter out and do regular water changes. And don't forget to acclimate your betta:) Let me know if you need any help.