I just went into flower with botanicare PBP soil (fox farms ocean forest as well). I normally dont add cal/mag seeing I use aerated tap water but since I've started flowering I add 1/2 of the recommended dose per gallon which is like 2.5ml just because I had a little funky def. pop up that looked like cal def. I dont know what kind of water you mean by the one you fill up at the supermarket but test it with a ppm/ec meter and see if it has any value at all, if it has a zero value I would add the cal/mag because theres no trace minerals in the water, so you'll have to add some. You can wait until you see a cal. def but you'll more than likely run into one if the water has no ppm/ec value.
I use the whole line though, I use the aqua shield with 2 root enhancer products, kanga roots and microbe brew from bushmaster. I think the sweet is an important part of flowering though, that I do recommend. I think you can get away without the other stuff but the sweet (I use the raw unflavored type) will add flavor and it will help feed what microbial life there is in the root zone (not much will be going on with synthetic nutes). But it will still add flavor. And as the person above said, add the hydroplex (the bloom enhancer one 0-10-6) throughout flower, I'd say follow the botanicare feed sch. on their website, use their numbers as a maximum until you get familiar with their product. However, I have yet to manage to burn my plants, I was actually under feeding them for awhile because I was unfamiliar with it and didnt want to burn my plants.