What are the MOST important things to test?

[Joe Tony]

Thank you all for your input. You've given me much to consider.

I think I'll probably just get the Hanna test kit for alkalinity, a refractometer, and get cheaper salifert kits for nitrates and phosphates. I currently only have four small coral polyps, and one of them is a mushroom, so maybe when I get several more corals, then I'll get a salifert test kit for calcium.

 

[vetteguy53081]

For reference:

 

[Randy Holmes-Farley Verified Community Expert]

IMO, alkalinity and calcium are essential, as are salinity and temperature.

Most everything else is case dependent.