as the weather gets colder your fish will become less active, require less feeding and if it gets cold enough they will gradually disappear till the weather warms up. I check my pond every day and if the fish are swimming about I put a pinch of food in the pond, but it really comes down to experiance, you soon get to know when the fish aren't feeding. as to the pump, some people will say keep it running 24/7 through the winter to prevent freeze up I personally run mine for a couple of hours every day to make sure the water is circulated and leave it at that and I've never had any major problems in 15yrs