In the marine aquarium world we do water changes to replace vital trace minerals and nutrients, and to some extent lower our DOC content. We don't use them to lower nutrients unless levels are drastically in excess.

In contrast, my planted aquarium needs water changes to prevent excess buildup of nutrients (when using the EI method).

However, if I am using calibration fluid (and comparative analysis using the water from my aquarium) and testing my aquarium frequently to ensure levels do not increase/decrease from optimal, why do I need to still do water changes?

Do I?

What benefit could the water change provide if my water parameters are already in check?

Thanks for your thoughts!