Your plants will likely need some of the nutrients found in the grow bottle, that are not found in the others. After the big veg stage it doesn't need as much nitrogen, and I believe less can also help it make the switch to flowering. But to keep the building blocks of life building they still need some of the nutes in the Grow Big, just not as much, and it also gets phased out again. Without the additional nitrogen you will end up with yellowing leaves as the plant taps its reserves and sucks what it has stored up out of the fan leaves.
Follow the schedule, but of course don't use as much as they say.