I have a friend who owns 10 goldfish (fancy) in a 10 gallon tank (for a few years)! When I first saw them, I just couldn't think of how much more you could get overstocked. Every time I try to explain the Nitrogen Cycle to him, he turns his back on me or just plugs his ears. How do I get him to listen or get new fish? Even worse, he has a TopFin 10 power filter at 7 gUS.