I have 5 platies (three female, two male) in a 10 gallon tank with live plants. It's been set up for about six months, and the water parameters are all fine. In the past few days, one of the female platies has developed a flat, almost concave stomach. She's acting normally though, eating and swimming just fine. I've read that the sunken stomach can be a sign of internal parasites, so I quarantined her to be safe. So does this sound like parasites, or something else? Should I try medication?