Without a TDS/conductivity meter its just going to be guesswork.....I
have one and I know precisely when and how much water to change so my
fish do not get shocked and I do not have unhealthy build-ups....well
maybe I do sometimes.....but I know about it though...........

Okay, I'll admit ignorance. Why is a TDS/conductivity meter such an
essential tool? Surely, not all dissolved solids/conductive ions are
harmful to fish. How would the readings be interpreted if used in a tank
with hard water or added salt? Is it more meaningful to concentrate on
reducing dissolved solids rather than reducing NOx and NHx?

-coelacanth