My experience with charcoal (if really activated or not, that's another issue) comes from the old days (when no water testing was ever made, no one ever knew about "the cycle", and
chlorine -not chloramines, was the only thing to worry) is to use it and replace it monthly, and remove it if medication is going to be used. I test -since my return to fishkeeping, for
GH and KH at least once a week, no big swings observed yet. Charcoal is not expensive at all, at least not for my small tanks
HOB filters.
Water does smell "worse" (not sure about the taste, no one addressed that in "drinking your tank water?" thread) without charcoal in the filter.
Pepe
Santo Domingo