So I have tried and with success, kept fish that I have caught. Examples of fish are chubs, bullheads, etc. But what i'm curious about is, when I have kept them in a tank for two or three days or so. The water starts turning an ugly brown. I caught chubs in a stream that is a bit muddy. So is mud excreting out of the fish? I have caught bullheads in a clear pond with lots of algae growth, but water still turns muddy and I do a lot of water change to try and maintain the clarity. Anyone got any ideas or tips? Thank you for your time.