I've noticed that too....
I do twice-monthly water changes, more often if I see the need. I don't
want my fish living in sh*t.


At what point do you "see the need"? What are your requirements? If you
are taking water measurements for nitrate, ammonia, or nitrite and these
specs are qualifiers for your "need" to do a water change, than you have
other problems. Your "need" to do a water change is masking a problem.

I have a feeling that your "need" to do a water change is purely
ritualistic.