Reef Tank Journals

I have a 210 Gallon tank, mostly soft corals, but am getting some LPS to grow.
I am running a 818 GEO Calcium Reactor. I also have a 75 gallon sump.
Just did a water test, everything was either at 0, or right on the number.
Only test that I couldn't do, was a Magnesium test, I don't have one, was told that you really don't have to test for that,
when everything else is doing fine.

So, here is the question,
I know a guy that runs a Coral shop, he ...