If I do not let the ammonia build up to some degree, how will the nitrites & nitrates form? I am asking to understand, not be contrary.
I did test my tap water for ammonia and it was at zero.
Ammonia occurs from the respiration of fish, and the breakdown of organics. There is thus always ammonia present in the aquarium, but the aim is to have it taken up fast by plants and/or bacteria.
Our test kits are not scientifically accurate to such a degree as to pick this up. We aim to have zero ammonia (and later zero nitrite) if fish are in the tank, because both of these are highly toxic to fish. While a level with our test kits of .25 or .5 is not going to outright kill fish (though some might), damage is still occurring, and fish that have "lived" through a cycle almost always succumb to other health issues and a shorter lifespan due to the long-term effect.
A fish-less cycle using pure ammonia obviously doesn't have the issue with fish, so we can raise the ammonia and nitrite. But not when fish are present.
The daily partial water change dilutes this ammonia and nitrite to minimize the effect on fish. But enough is still present to keep the bacteria and plants happy. We call this "silent cycling," because you don't see it via tests, and the fish experience (so far as we know) no detrimental effect. As I said initially, fish are continually releasing ammonia by respiration, but if this alone were sufficient to kill them we would never have live fish in any aquarium. Fortunately the plants and bacteria grab this before it has time to weaken the fish.
But having said that, the more fish or the larger the fish per water volume, the more chance there is of ammonia poisoning. The larger the tank, and fewer the fish, the safer.
Does this help?
Byron.