I have him for about a month now, before I got him he was on meal worms and now I feed him pellets and beefheart. His black is showing more than before. I do water changes every 2-3 weeks 20%.my silver looked like that (black fins) when I got it (24") but I started feeding it better foods and the pinks/orange/teal colors came back. What has your freind been feeding that fish, and what is the tank maintenance like?