Whoa! yeah, get the Betta out of there. The Betta is not what you have to worry about. Give the oscar another month to grow and your betta will be dessert. A 55 gallon is a good size for oscars, but not optimal for bettas. Bettas like virtually still water and a 55 gallon is going to take a bunch of water flow for proper filtration. The best tank I have found for a betta is the 3 gallon Tetra Whisper Aquarium. The filter allows you to adjust the water flow to low low settings for the fish. Betta fish are "fighting" fish, but that is among their own species. They usually end up a target in a community tank because their long flowing fins are irrasitable to other fish. They love to nip fins. If you would like to learn more about bettas, contact me. I am a big betta fan. Best of luck.