Equilibrium is for water reconstitution, turning RO water into a freshwater approximation.
Flourish is a Micronutrient fertilizer.
They are designed to do different things. In order to understand their functions, I'll compare them to Greg Watson stuff. Equilibrium plays the same role as Barr GH Booster. Flourish plays the same role as CSM+B or TMG.
As an example: I start with RO water. I add Equilibrium to give it a proper GH, along with some other minerals. Now I have "fresh water" with a proper PH. I add baking soda to increase the KH. I add this new water to my tank during water changes. I fertilize my aquarium with KH2PO4 and KNO3 (macros) on Monday, Wednesday, Friday. I fertilize my aquarium with Flourish (micros) on Tuesday, Thursday, Saturday.