Over the past couple weeks 3 of my platys have died and I'm not sure why at all. My ammonia and nitrite are both 0 and my nitrate has been a bit high about 50ppm, but I'm doing water changes to get it back down. But the platys have had way worse levels before bc they went through the cycling of the tank before I knew about such things. I had them for 11ish months. The first two just died out of the blue with no signs of sickness or anything. The third's fins started to appear torn/dissolved/damaged shortly before he died. None of my other fish are showing any signs of disease. If anyone has any ideas of what could have happened that'd be great!