Most fundamental important water tests:

[Rupture Reefer]

What in your opinion are the only necessary water tests for an LPS and Softies reef tank?

 

[Flippers4pups]

SG, alkalinity, calcium, magnesium, phosphate, nitrate, pH.

 

[RMS18]

Almost everything listed above outside ammonia and nitrite as you shouldn't have these if your tank is cycled correctly. Alk, Mag and Cal are what corals use to grow especially stony corals (LPS) it's the fundamental 3. PO4 and PO3 are good to know so you can prevent algae issues, corals do need both to grow, we call these "nutrients". LPS and softies prefer a dirtier water than SPS so these levels can be elevated a bit more but on younger tanks it's good to keep an eye on them for algae issues. Salinity is very important, stability is key. DKH is a measurement commonly used to measure ALK. PH is also good to know, you want to minimize the swings PH may take. Large swings of PH may be associated with a ALK issue, such as low ALK.

 

[fish farmer]

SG, alkalinity, calcium, magnesium, phosphate, nitrate, pH.

All these, but I didn't test nitrates and phosphates regularly for a while and my softies did fine as well as a hammer.....my GHA did awesome as well. Now back to testing weekly. I just picked up a Mg kit since I rarely did that, but have been having low Ca for a while(under 400), is is a little below 1200, so I'll be keeping an eye on that as well.