When the water temperature in the pond drops below 50F degrees it's time to completely stop feeding your goldfish and koi for the winter. The metabolism of fish slows drastically at this point and the fish cannot properly digest Protein based food. Also, your biological filter is becoming less active and cannot break down the food and ammonia. If you feel you must give them something, buy vegetable based food, and feed sparingly. Better yet, feed fresh vegetables. Any soft vegetable should be fine. Peas, cucumber and melon work well and a fish favorite is Parsley on a stand. We make stands by drilling a hole in a flat rock and epoxying a short piece of dowel rod into the hole. Wrap a couple of rubber bands around the head of Parsley and slide it onto the post. Drop it into the pond and watch your fish strip the Parsley Tree clean.

Feeding should be delayed as long as possible in spring to allow your bio-filter to re-establish itself.
The Bio colony starts growing when the water temperature rises above 40F degrees. It gets continuously more dense and effective as the temperature climbs. The peak effectiveness can take 3-4 months, but can rise more rapidly with the addition of a bio booster. Numerous products are available including Pond Magic, a bio booster that is combined with enzymes and trace minerals. A small amount of this product added weekly to your filtration system will boost culture growth rate and it's effectiveness.