Mr. Sharpey-
If it ain't broke, don't break it. If it's bent, get it straightened out. Now, if it is water that has been housing fish without filtration for months because the temperature is below freezing, then as things begin to warm up and our fish begin to start moving again, well, change the water.
There is a temperature window of water in the 40's and low 50's where the metabolism within my pond is more toxic than beneficial. I see water changing as almost the only fish health tool available. My well water is 52F, which is ??C, so at about 45F pond temps I can start changing small amounts of water. Because I have an overflow, all I really do is add water, creating overflow to expel the oldest bottom water. Also at about 45F, I'll be able to start the skimmer to waterfall circuit with about 1200gph flow because my pond will still be covered. By the time the pond water is at 50F I will be adding/changing 5-10% a day and will do this until filtration kicks in in about a month, no seeding needed.
The cover will come off when night time temps are reliably above 40F which for us up north can be JUNE,

well mid to late April really.
Interesting thing MikeM brought up about the PH. Water here is jackhammer hard and PH has never in any pond or tank or aquarium tested anything other than 8.2. Maybe checking the 37F water right now will give me something lower? Cool.
Stevedore Sputnik-
I don't have to deal with chlorine or chloramines, but I think that if I did I would use a reservoir tank. The filled tank could be treated for the known gallonage, could be aerated, could be temperature acclimated, and then cold be drained into the pond to refill or to overflow. Also, my limited knowledge is that Chloramx powder is cheap enough, and will address more than just the chlorine, say if there were chloramines in your water or if there were ammonia or nitrite build up as your filter comes online.
Mickey the windowman