Water soluble fertilizer application question's

So i’m getting into trying to learn how to use nutrients. My plants are in flower and im assuming they’re running low on nutrients since they’re looking a little sad. I’m just curious how water soluble nutrients work. I know there’s instructions on how much to mix per gallon of water but im just curious how to apply and when. It suggests every other watering on the Fox Farms “Grow Big” bottle i have. Do i soak the whole pot in the nutrient water like i would for a normal watering or should I do a 50/50 between chlorinated regular water and the nutrient water? Also for using multiple nutrients like a combo of Fox farms Tiger Bloom, Grow Big, and Big Bloom how would I go about incorporating those? Would I have to mix all 3 in their own separate gallons and then water all at once and do like 1/3 of each per plant?? Very confused so anything would help thanks!