Yes hardness and alkalinity are not identical but scale is similar 0 to 400 and the difference is not easy to understand. Here is a good analysis.
https://srac.tamu.edu/serveFactSheet/112 Hardness is traditionally measured
by chemical titration. The
hardness of a water sample is reported
in milligrams per liter as
calcium carbonate (mg/L CaCO3).
Calcium carbonate hardness is a
general term that indicates the
total quantity of divalent salts present
and does not specifically identify
whether calcium, magnesium
and/or some other divalent salt is
causing water hardness.
Hardness is commonly confused
with alkalinity (the total concentration
of base). The confusion relates
to the term used to report
both measures, mg/L CaCO3.
If
limestone is responsible for both
hardness and alkalinity, the concentrations
will be similar if not
identical. However, where sodium
bicarbonate (NaHCO3) is responsible
for alkalinity it is possible
to have low hardness and high
alkalinity. Acidic, ground or well
water can have low or high hardness
and has little or no alkalinity.