Over the last week she has developed a pale patch on the bridge of her nose and a few more patches over her entire body, her tail also looks a bit tatty.
She is still very active and has a healthy appetite
The water quality is fine. The only change I have made is to add another smaller female to the tank (about two weeks ago). The other small female and the male look fine. They are the only occupants of the tank.
Any ideas? It doesn't look like fighting wounds to me but I could stand corrected.