I have a very large pond and have raised 10 gold fish and two alge sharkies for about 2 years. About 4 days ago, all of my fish disappeared. They used to come out when fed and I would count them to make sure all of them were there. All of a sudden one of them came out from under the liner flap and darted around then disappeared. I thought I saw a new baby, but even my sharks are hiding. What could be happening? The weather is warmer with very cold nights but my fish have been in a stable environement for over two years. The only thing I did was clean my filters, which I normally do. Any thoughts?? These are my pets and I don't want to lose them.