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Be sure to time your water changes so that your changing as late as possible in the fall (on a nice day) and as early as possible in the spring so you never changing in the winter.
Id agree with clover. If the water is OK, then leave it.If the water has gone bad, then change it.If the temperatures are so cold and your'e really worried about freezing, maybe leave the pumps running and change only half of it.Whilst they say this is false economy, it will give a fresh lease of life to the water until the weather turns.We don't particularly have really long cold spells here in the UK.We could be -10°C for a week, then +10°C a week later.My scheduled water change would wait for the warm spell.