I'm all about the good bacteria in the water and your bio-filter in my ponds. Use only dechlorinated water to rinse anything in your pond. Chlorine will kill any good bacteria. These good bacterias are awaken in warm temps (not sure of the temp).
In my ponds, a ten year old 550 gal one and a new 1100+ gal one since last summer, they have been healthy and I never change water, and I only just add filtered water or small amounts of timed sprinkler water.
Personally I wouldn't do anything until the temps are higher for longer periods of time. But to me cold is 60* or less. Remember this is my opinion and I do live in Southern California where the fish in my pond are constantly begging for food.