Seems like most of us dose a 2-part Ca/Alk system - likely very much similar [if not same] compounds. One store bought, one made at home [from non-LFS compounds] ... but same solutions, in essence.
I've used both B-ionic systems and Randy's 2-part [really 3-part, with Magnesium additions] and IMO they're quite similar product [and the same concept, adding Ca from one bottle, Alk/Carbonate from the other to balance these 2 levels in the tank].
While possible, I suppose someone is just using water changes, or just using Kalkwasser too ... just seems that 2-part is most common [other than the most common Ca Rxs]
Just my take on it. Depending on tank size, you could make it quite a while. My 58g after a couple years now slurps up the 2-part ... but while growing out frags, it really didn't cost that much.