I noticed my double tail betta had rips in his top fin and tail a couple day ago. I assumed they were tears or he bit his own tail. The top fins look better today but the tail didn't get better; also the tear spot looks a little brown. Do think this is fin rot? The top fin is not as ragged anymore as it looks in the picture.
He lives in a 2.5 gallon, heated, filtered tank by himself. The only other live things are two marimo balls.