Like Watermom said, it's easier -- if you have the K-2006 -- just to run higher chlorine, than to add in another chemical.

Regarding cal hypo, anything at 65% or above is fine. Usually the 65 - 68% strength is a better deal. The 73+% strength is just made with a somewhat refined process. But, avoid the products below 65% -- as far as I know, they are all blends, with mystery ingredients. They are almost always LESS economical, and sometimes the mystery ingredients cause problems.