I've had my pond, 8 ft. X 4 ft. 30 in. deep, since 2008. I added fish in 2009 and they have wintered nicely, even producing fry in 2012. My ongoing problem has been a drastic loss of water, but only in the cold of winter. Until winter of 2013 I ran the pump and waterfall thru the winter to oxygenate the water. The water loss suggested to me that the filters were clogged and that the pump was pumping out but never making it through the filter/waterfall. But turning off the whole pump/waterfall system last winter and this (I use a heater when necessary) did not remedy the problem. A few weeks ago, when the pond dropped 10 inches I topped it off. Within 12 hours it had returned to 10 inches low. Since then it has dropped again, now by 1-1/2-2 feet.

I'm mystified. This never happens in the spring, summer, or fall.