I don't know about that....but when I went to buy "free chloro" this past time, I was told that none was available on the North Coast. I was told by the owner of the store that one shop on the North Coast was selling what they called free chloro, but it wasn't it at all. They also said that the "free chloro" (and maybe the tablets as well....I don't know) come from China and that there had been some problem getting it lately.
I personally don't know anything about pool chemicals. I just rely on the gentleman who owns the supply store and this is what he told me.