I think your a bit confused by your test kits and their meanings. The
jargon is here to help you. Your local area should have water quality
printed and sent to you annual to verify this.

Alkalinity is the same as kH as well as total carbonate hardness. It
is not possible with drinking tap water to have these true values vary
to any appreciable degree. That means concentration of carbonate
[HCO3-] is essentially all your alkalinity.

Hardness is the same as gH as well as total hardness. This is a
different value than alkalinity! It is express as amount of equivalent
CaCO3 found in water from determining Ca and Mg levels in natural
waters.

I like Seachem products from changing kH and gH since they are
inexpensive and use a reasonable blend of salts.