Cultivation Nation is a 2 part synthetic feed program that contains a veg formula and a flowering formula. It's available in both dry salts and liquid form. It's intended to be used together. The Big Bloom has zero nitrogen in it. While flowering plants don't need much nitrogen, they still need some. If it were my grow, I would skip the "Big Bloom" and use the Cultivation Nation flowering formula like Fox Farm intended.
P.S. I've used Cultivation Nation dry salts in previous grows without any issues. The 2 formulas plus cal-mag during flower should be pretty much all you need to cover your plants' nutrition.