First, this is only for pour-over and not espresso. Espresso has other issues related to hardness (scale for one) that don't concern pour-over. I use carbon filtered tap water that is medium hard....160 ppm total hardness and relatively high alkalinity...120 ppm. For pour-overs you hear quite a bit about the benefits of relatively soft water. My question is if the concern with total hardness is more to do with it almost always being accompanied by high alkalinity which I know can be a problem or is there an issue with Ca and Mg levels independent of alkalinity? When you build your own water this is not an issue because you can choose your components but with tap water high hardness very often comes with carbonate alkalinity. I use phosphoric acid to reduce alkalinity basically converting calcium carbonate to CO2, water and calcium phosphate. So I get my alkalinity where I want it (I use water composition software and empirical testing). The Ca/Mg levels stay the same...50 ppm Ca and 11 ppm Mg. Is there a positive or negative effect of these hardness components when alkalinity is not an issue? Should I also test with dilution to get lower Ca/Mg levels at the same alkalinity I adjust to now? I suppose the people who could best answer this are ones that build water from distilled with low or no alkalinity but have experimented with Ca/Mg levels for pour-overs. Just for completeness, I brew almost all medium-light or light roasted dense coffee. Thanks.

or is there an issue with Ca and Mg levels independent of alkalinity?

60 ppm total of both Ca and Mg is a good place to be in my opinion. This doesn't show up within the error bounds of a consumer refract, but increasing hardness seems to give the illusion of tasting a higher extraction for me. Ca and Mg ions taste different for me, but neither one is better for everyone. I have been happy with total GH values anywhere between 15 - 60 ppm as CaCO3, but I do change my other parameters a bit when dialing in. Right now, I don't like much more than 60 or 70 GH personally

Alkalinity I don't generally like more than 30 ppm as CaCO3 for filter. Anything below that I generally like.

I am a bit confused. GH is a measure of Ca and Mg cations only and mine would be 58. My total hardness as CaCO3 is 160 ppm which I believe is GH+KH because KH only measures the anions HCO3- and CO3--. So when you say GH as CaCO3, I'm not sure if you are referring to total harness as CaCO3 or to GH. No big deal, this may be more than I want to tackle!

Yes, GH is a measure of total hardness - - essentially both Ca and Mg ions in units of chemical equivalence. It is not the sum of the mass of the ions though, but rather the sum of the chemical effect of the ions, expressed in some unit of chemical equivalence. German degrees, French degrees, mEq/L, and mg/L as CaCO3 are all units of chemical equivalence. In your case you have 50 ppm of Ca ion, which is a chemically equivalent to 125 mg/L CaCO3, which is your calcium hardness. And you have 11 ppm of Mg ion, which is chemically equivalent to 45 mg/L CaCO3, so that's your magnesium hardness. Then you add these to get 170 mg/L of total hardness as CaCO3. This is what you would get from a GH titration test kit which measures the number (not the mass) of those hardness ions.

KH is a measure of alkalinity, based on the number of protons (H+ ions) that the acid buffer (e.g., bicarbonate and carbonate) in the water will neutralize. It is also expressed in units of chemical equivalence like CaCO3 equivalent.

You generally can't add GH and KH to get a meaningful result. If both hardness (GH) and alkalinity (KH) are expressed in the same units of chemical equivalence, then it's sometimes useful to compare the two. Your actual carbonate hardness is the lesser of those two measures. In the case of natural water, GH is almost always greater than alkalinity, so that's why test kits that measure alkalinity often referred to as measures of carbonate hardness. All popular KH drop titration test kits are actually simple alkalinity test kits.