My 4 goldfish seemed to be having a hard time staying down at the bottom for about 2 days. I thought maybe i'm over analyzing until i noticed they were trying to scavenge at the bottom and their butt would act like a balloon an start to bring them up. I thought it would be best to just go with the pea option to rule out swim bladder. I fed them peas and now they seem so much better. But their poop is a black color. I was wondering if thats normal.