I just don't understand the motivation to not do routine partial water changes.
Time, effort, money, bad source water???
EXPERTS ALL AGREE that routine partial water changes ensure the best water chemistry and quality in the aquarium. I'm 'all in' for an eco-system setup that aids in water purification...lighting, plants, filters, substrate, bottom feeders, snails... and perhaps this can result in less frequent or reduced volume of water changes.
However, there simply is no denying that a continued routine partial replacement of old tank water with fresh, clean, pure water is beneficial.
The ideal system would be a drip/overflow system where fresh, pure water is constantly entering the system, replacing old water. Second to that are our weekly or bi-weekly partial water changes with pump or siphon and refill hose or buckets.
To the member that said we don't do water changes on lakes. Nature does, it's called rain and rain runoff. Sometimes the water is filtered through the soil, picks up calcium, magnesium etc. and enters a body of water through springs. Sometimes it's creeks, streams and/or river inlets and outlets. The point is that nature is doing partial water changes all the time...and just as we say that larger tanks are more forgiving, so are the larger ponds and lakes.
Some say their ammonia, nitrite, and nitrate levels are zero-low. But we simply do not have the resources to fully analyze tank water to determine purity.
A well developed 'nearly natural' eco-system can help maintain higher water quality but nothing eliminates the need for pure, fresh water replacement.