This discussion has ranged widely and covered some very useful ground. The initial point was, if I remember, frequency of water changes.
Two considerations that are rarely brought up in these and related threads:
---The importance of minimizing DOC and TDS/TSS. Besides ammonia, the decomposition of feces, food and dying plants injects dissolved organic compounds into the water. This is not filtered out, nor is it converted to anything else.
---Total dissolved solids include the above, but also minerals, chemicals and anything that you put into the tank besides water, and anything that's in the water that you put into your tank.
Both of these parameters are difficult to quantify without specialized equipment.
Also important is re-mineralization. Livestock and plants use a quantity of certain minerals, most of which need to be replenished through regular water changes.
More experienced keepers than I have addressed this subject more capably.