I woke up this morning and found that my blue gourmi was black from the tail to its gills, or close to it. You can still see the stripes in his body, but all fins have turned black too. The pattern of the fish is in tact, but where the body should be blue, it is black. It has had some scratches/bites on his side and belly, and that is where the black starts/stops. I did a 33% water change, anything else I can do? What is this color change? Thanks for any/all help.