Hello, I have a small Black Moor in a 10 gallon aquarium, right now he's about 1" not counting his rear fin. In the last week he has rapidly turned a gold/silver color over more then half his body, his head seems to be a light brown. From what I've read online this is fairly common in older fish, but seems to occur at a much slower pace. A week ago he was almost entirely black with a few shiny gold scales on his belly. Now he looks like this, also today I noticed part of his rear fin was missing a chunk. Does any of this sound normal, I'm new to fish keeping and trying to do the right thing. I'm using a Penguin Bio-Wheel Mini, it's been keeping ammonia at 0, I don't believe water quality is an issue even though I've been told my tank is too small for a goldfish(not sure I believe it, maybe when he's full size). Thanks - Derrick EDIT: I just checked the water parameters, I'm using an API Freshwater Master Test Kit(drops). pH: 7.6 Ammonia: 0 Nitrite: 0 Nitrate: 80 Did a 50% water change due to the Nitrate, and added stress coat.