Water Exchange Question

The other day I pumped out about 4 - 6 inches of water from my pond and then
refilled it. I did the same thing the next day. I wanted to get some fresh
water in my pond and figured that was a better way than just overflowing the
pond, which is what I did in the past. What I want to know is: how many
days can I keep doing this without harming my fish? I would like to keep
doing it until all the water has been exchanged without having to remove
fish from the pond and removing water all at once. Earlier in the season I
did some vacuuming in the pond and the bottom is fairly clean. But the
water has been in the pond for 4 years with only fresh water being added
when I overflowed the pond. Fish are fine and healthy and acting normal.
The fish load is such that I think a total change of all the water would be
a good thing.

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~~~Politicians and diapers have one thing in common. They should both be
changed regularly and for the same reason.~~~