It’s interesting to note that in the brs video, the Red Sea mixes had a fair amount of drop in alk and ca compared to the other 6 mixes. Your experience seems to be the opposite of what they found. They didn’t test fritz but they did test both rc and rs blue.
The coral pro (black bucket) moved significantly.
Blue bucket moved a little, not much, and it was close to within the error resolution of the Hanna checker to be not that significant. Plus I haven't gone more than 2 weeks before using my salt mix.
Reef crystals was fine for me as long as my bucket was clean. I believe BRS washed and cleaned all their but jets prior to testing.