20 gallon long, fully cycled tank. 1 male swordtail, 1 male Molly, 1 male betta I'm interested in getting Cory cats for my tank but I don't really know much about them. How many would you keep in a 20 gallon tank? What is the minimum tank size? Would they be ok with the fish that I have? Mostly concerned about the betta, the molly and swordtail are larger than he is so he has not bothered them for the couple of months they've been together. I know that he will eventually attack smaller fish than him. Tried dividing the tank but somehow the other fish get on his side every time.