Tom i thought your water already have a GH from tap
Yes, 2 degrees, about 35 ppm or thereabouts.
I still add more Gh booster.
Shalu used to go nuts with GH booster, hitting 9-10 degrees, his colors and fish looked awesome.
I do not know, I suppose I could lard more in there, but I'm not really going to get more growth, eg, the ppm's are non limiting, but they may enhance coloration more in some species.
I tend to dose a KNOWN Gh booster for the Mg and the added K+, less for the Ca and SO4 etc.
Now I could add MgSO4 to the trace mix and then mix some K2SO4 into the KNO3, but it's not much hassle and added Ca++ never did no harm in any plant species I've ever kept. Or I could test the tap all the time and dose based on those results, which frankly, its way too much hassle when a simpler solution is available. I'm good at knowing what Mg limitation looks like, I learned the hard way 15 years ago. PMDD helped me a lot.