I do not know if this will be of help to anyone that uses lots of Calcium and magnesium but here it is for what is might be worth.
I used to be very much involved in keeping saltwater fish and corals.
My largest saltwater tank was 390 gallons.
The saltwater hobby uses lots of calcium and magnesium.
Here is a link to how to make calcium and magnesium additives that, I would think, should also work for plants.
Read carefully, and maybe someone can give some additional figures for safe use in plants.
Do-it-Yourself Two-Part
Calcium and Alkalinity Supplement System
I used to be very much involved in keeping saltwater fish and corals.
My largest saltwater tank was 390 gallons.
The saltwater hobby uses lots of calcium and magnesium.
Here is a link to how to make calcium and magnesium additives that, I would think, should also work for plants.
Read carefully, and maybe someone can give some additional figures for safe use in plants.
Do-it-Yourself Two-Part
Calcium and Alkalinity Supplement System