I have a male betta in a 10-gallon tank with 6 neon tetras. They've been in the tank together for about 3 weeks now. Water is changed 50% weekly, with last water change 2 days ago. He's still swimming and eating normally, but his fins are...well, for lack of a better term, frayed. Not like nipped at the ends, but they're starting to look like fringe from his body all the way out. What is going on here? Do we need to get him a small tank all his own? HELP!