Hello, I have had my goldfish for about 3 years. He is living in a 10 gallon aquarium. Lately he has been staying at the bottom of the tank, nor moving around a lot. We thought that he might have swim bladder, so we tried fasting him for a few days. It didn't seem to help. I cleaned his tank today and no improvement. It seems to me that his breathing has slowed, and the top half of him seems darker almost greyish-black. Is there anything we can do for him?