Can anyone help me figure out why my platies are dying for no apparent reason? I had 7 platies and a pleco in a 75 gallon tank. I have had the tank set up for 2 and a half months and it has been cycled for a month now. 2 days ago I found 1 platy floating on the top completely drained of color, and this morning I found another the same way. Water parameters are 0 ammonia, 0 nitrite and 5 nitrate, I haven't added or removed anything from the tank since I started it and all 7 platies have been in from the beginning. Any idea what could have happened?