I change 5-10 litres every week in a 70 litres aquarium. + I add the water that evaporated. Sometimes, but rarely, I don’t do the water change. It’s because I get water from my father, and sometimes I can’t visit him.
I also have an external Aquael FZN-1 filter set for maximal flow (500l/h for a new flter, not sure how much is it now – I don’t clean it).
Much of the work is done by Ceratopteris, Vallisneria and other plants, so the water quality is really nice. I also have java snails to clean up, and helenas to controll the former population.