I change 20g/75g=26.6% first weekend of every month. This way I am able to keep a stable system easier with the two part.
I believe water changes in themselves can be just as much turmoil as anything else, becaue lets face it, I doubt most take the time to prep the water days in advance and "perfectly" match it. If you are, congratulations keep up the good work, I think you are the minority. In the end, that rapid shift could be potentially dangerous, though to a very small percentage of risk.
Though I am not condoning no water changes or more, I have found this system has worked best for me to maintain stability the easiest.
I think water changes are kind of a "do-over" when your nitrates or Alk/CA get out of balance, and to refresh trace elements. But all three have been found to be controlled otherways. So I guess the real question is....Have we gotten to the point chemistry speaking not to do any? We have all heard of those unicorn tanks that don't get changed....ever.
If some are under the impression that the water gets old, well you are replenishing with top-off, so in theory if your tank is "really" in balance, ie: nutrients in and out, then water changes should, and I say "technically" not be necessary. Because the water is as fresh, clean, and stable as when you changed it last.
If you have a hard time with daily husbandry, then yes more water changes the better. I do believe there was an article about doing little water changes frequently or large ones infrequently, or infinitly ie: constant supply, here on RC. But can't remember why, but thats part of the reason I do only change once a month. Anybody know the link?