My Goldfish has been acting strange these past few days, he's been lying on his side most of the time like they do when the fish are dead. He is just floating around, not swimming and just bobs around the water, i try to put food near him he is eating a small amount but not as much, he is still breathing, the other fish are doing fine, and the water is fine. I am just wondering what the problem could be? and what the best thing is to do? Many thanks.