I have had a black molly in my tank for about one month. My tank is only 6 weeks old. He seems healthy and has been growing, but lately the tip of his large fin on top of his body has turned yellow. Also the scales on the side of his body have turned white. This does not resemble "ich", as I have seen pictures of it. Does anyone know what is going on? By the way all of my water tests have been good for about 10 days, but before that I had high nitrites for about 2 weeks.