I have a small school of neons, but it seems to be getting smaller. About a week ago I noticed that one of my neons' tails was losing the red and turning white. I did a 25% water change, and all the levels look fine. Well he died. Today I noticed that another neon had the same loss of color in his tail. It looks like the red is being bleached out. The blue stripe on top stays very bright, but the red disappears. My water is testing fine and no changes have been made to the tank. Is this a neon disease or maybe a sign of old age in neons?? The water temp is 78-80 degrees, and I feed them a diet of flakes and dried tubifex. Anyone ever see anything like this?