Gypsum is the common name for calcium sulfate, a very water-soluble form of
calcium. If you want to add that, then apply gypsum.

Thanks for the explanation. I needed to add calcium into the soil.
That was the reason why I used gypsum, and I did that last week.

What's your PH?

The pH in that part of the soil is acceptable according to the soil
test recommendation sheet that I received from a soil test center. I
don't remember exactly what the pH value is. If you want, I can look
for it when I get back home.

The soil test recommendation sheet asked me not to do anything on
changing the pH. Instead, it asked me to add calcium sulfate into the
soil to increase the calcium level (because the calcium level is low).

Next year, I will use some cheap soil test kit to monitor the pH value
of the soil. Sending out to soil test lab that can get expensive; I
can only do that every couple years.

Jay Chan