All of them matter and you should keep an eye on them consistently for stability. Depending on fresh or salt you will need to add a couple others to the list as well. I recently went through some issues with my tank parameters and discovered my ALK
and Mag were low..and honestly In the first 6 months of my tank I never tested for mag,ALK
,calc one time. Once I fixed these issues my tank perked up and now I keep an eye on everything.
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