I didn't watch the video you posted, but following direction from another video, I made a vinegar/eggshell calcium solution. It was pretty easy.
I crushed a few dry eggshells by hand and put them in a stainless steel skillet. I gently toasted them while continuing to crush them into smaller bits with the bottom of a small bowl
When they started browning I took the pan outside and blew all the dried chaff away (the eggshell membrane).
I added the toasted shells to a small jar, then added apple cider vinegar, approximately 10 parts vinegar to 1 part eggshell. It began bubbling immediately.
You can strain the vinegar from the shells after 10 days, but longer is ok. The calcium in the solution is supposed to be readily available for plants to use. And I guess it's pretty potent because according to the video, you mix the solution with water at a ratio of 1 part to 1000 parts. I think that's a little less than a teaspoon of calcium solution per gallon of water.
Here's a link to a PDF that explains the process and its use.
https://www.ctahr.hawaii.edu/oc/freepubs/pdf/SA-10.pdf
Thanks for all that great info. I will read that PDF and maybe give it a try.