Since 2 days my female platy just hangs out near the surface. She doesn't look like she gasping for air but just to be sure I increase my filter speed so more oxygen gets in there. I do 20% water change daily but today I did a 40% change to clean the gravel etc. The 2 other fishes seem to be fine. She doesn't have any spots, parasites or anything. She doesn't really eat since 2 days either. She looks like she's missing a little bit of fin or her tail. Probably from when my betta was harassing her to first day she was in. What could it be?