I have a female platy that I think is sick. Her gills are open more than usual, she swims around the surface almost gasping for air or she sits on the bottom. I believe she has also lost her appetite. I think she may have gill mites or fill flukes. I didn't notice this until I put more fish into her tank. I also have a nerite snail in there. What treatment should I use that would help her but not harm the other fish or my snail?