Per Joe Formanek in response to my question about chelation of Ca by BTB:
“Dove further into this, and found that Tannic acid does not form complexes with Ca. The only thing you can expect to happen is ordinary salt formation. Considering that tannic acid is a weak acid the latter will only occur provided Ca is present as Ca(OH)2 or as a salt of an even weaker other acid.
Since “tannin” and “tannic acid” are often used as synonyms, even in scientific literature, there often is ambiguity about the botanical origin and chemical composition of the product in such references. This is important to keep in mind as calcium tannate in tea, which is sparingly soluble, is chemically not the same thing as the calcium salt that could form using Brewtan Tannic acid.
So - while you might have a calcium salt form if a solution is dehydrated, the actual coordination and chelation of Ca ions does not occur like it does for Fe.
Hope this helps!!
Joe”
And I hope this helps, too. Cheers!