I have a female guppy I recently acquired that's lips look white and crusty. It doesn't look cottony, just crusty. I just noticed this today and have had her for 2 days. No other fish in the tank has this problem or any other, everyone else seems fine. The guppy's mouth has been staying open all day and hasn't seemed to close shut, and the guppy is acting lethargic. Does anyone know what meds I should use? I had a male guppy that had this same problem a month ago in a different tank; he died the day after I initially noticed the crusty appearance on his mouth.