Any LPS? Clams? Crustaceans? If no calcifying corals, then you really won't need to worry, because Alk, Ca, and Mg aren't being consumed by the corals. As long as Alk stays above 6dKH, it will be fine.
Assuming you do water changes and maintain salinity with RODI topoff, those parameters will remain within the guardrails. I would focus on managing salinity, nitrates, and phosphates instead.